Research into the cause and possible control methods of increased growth of periphyton in the western basin of Lake Ontario

Transcription

1 Research into the cause and possible control methods of increased growth of periphyton in the western basin of Lake Ontario Summary Final Report For Ontario Water Works Research Consortium In fulfillment of a Research Agreement between: The University of Waterloo and the Ontario Clean Water Agency (OCWA) on behalf of the Ontario Water Works Research Consortium by University of Waterloo Cladophora Study Team: Robert Hecky, Dave Barton, Dave Depew, Stephanie Guildford, Scott Higgins, Veronique Hiriart-Baer, Adam Houben, Luis Leon, Sairah Malkin, Kirsten Muller, Tedy Ozersky, Sarah Ross 1

2 Executive Abstract In response to complaints of residents of municipalities along the northwest shore of Lake Ontario concerning beach fouling caused by excessive benthic algal growth, the Ontario Water Works Research Consortium (OWWRC) asked the Ontario Clean Water Agency (OCWA) to coordinate a study of the problem. OCWA signed a research agreement with the University of Waterloo to conduct studies from with five objectives. This report summarizes all the studies (Summary Report and 12 appendices) undertaken to address the objectives and gives major conclusions reached relevant to the five objectives of the agreement. 1. Determine whether periphyton biomass is increasing. The amount of benthic algal material (periphyton) produced per unit of length of shoreline has increased since the early 1990 s when dreissenid mussels became established in Lake Ontario. One species of periphyton, Cladophora glomerata, is responsible. This same species was the cause of shoreline fouling in the 1960 s and 1970 s, but its growth had been reduced with the introduction of phosphorus controls following the Great Lakes Water Quality Agreement. Phosphorus concentrations today both offshore and near-shore are at all time low concentrations yet Cladophora biomass has unexpectedly increased. This recent upsurge suggests that growth conditions for this plant have recently changed. 2. Establish the sites of excessive growth of noxious species and, if possible, the specific sites that contribute to on-shore complaints. Cladophora grows on rocky or other hard substrates where light and nutrients are available. The depth limit for growth given suitable rocky substrata is set by water transparency which has increased, especially in coastal areas, after the establishment of dreissenid mussels as their feeding by filtration removes small particles from the water column Surveys were done along Lake Ontario shorelines as well as Lake Erie shorelines to determine the general distribution and abundance of Cladophora. These surveys determined that growth along rural rocky shorelines could be as heavy as along urbanized shorelines. 3. Investigate the causes of increased biomass and changes in species composition. A successfully validated Cladophora growth model was developed that can predict the development of algal abundance per square meter through the development of maximum biomass given necessary input data on temperature, light availability and internal phosphorus concentrations. The model also can simulate well the timing of detachment events. The model was used to determine how algal abundance now differs from historic conditions. The model output demonstrates that because of increases in transparency Cladophora grows to greater depths now than in the past and the depth of maximum algal abundance is greater than historically. Per unit length of shoreline (along rocky shorelines), the total production of Cladophora can be nearly as great as in the 1980 s but is still below the dense nuisance growths that fouled shorelines in the 1970 s prior to the P reductions at point sources. However, current estimates of maximum biomass per unit area is lower and further offshore than historic estimates. The maximum biomass per unit area is still lower than historic estimates as is the internal phosphorus (P) concentration in the plant indicating that P still limits benthic algal growth, and P 2

3 availability limits the maximum biomass attained at depths where light is saturating for algal growth.. 4. Determine the impact of local sources of nutrients, including wastewater plants, on biomass production. High resolution spatial surveys of Cladophora abundance along Halton shorelines that included inputs of major streams, waste water treatment plants and storm sewers could not detect any impact of these local inputs on Cladophora growth patterns. The explanation for this lack of relationship is found with the dreissenid mussels that now continuously cover rocky substrata in Lake Ontario and even extend on to soft bottom substrata. Measurements of phosphorus excretion by these mussels indicate that mussels are now the dominant source of readily available phosphorus in the coastal zone. The mussels feed on phytoplankton and particulate matter. Coastal waters are efficiently flushed with offshore waters during the period of rapid growth of Cladophora. The offshore water provides phytoplankton (microscopic algae) that are consumed by the mussels, and the phosphorus (P) contained in this consumed phytoplankton constitutes a new near-shore benthic source of soluble phosphorus to support growth by benthic algae. With an adequate supply of P, Cladophora dominates over other benthic algae because its upright and filamentous growth form lets it compete well for light while increasing the plant area for uptake of dissolved inorganic carbon that can limit photosynthetic rates in microscopic benthic algae. 5. Advise on possible control methods Dreissenids have re-engineered the near-shore coastal zone by increasing light transparency and providing a new benthic source of available P to support benthic algal growth. The impact and persistence of this re-engineered environment is dependent on the abundance of mussels. Unless there is a new control imposed on mussel populations, for example by disease or a new predator, the present situation will persist. The mussels regenerate soluble P that ultimately comes from their food source that is predominantly phytoplankton from the lake. Consequently depending on the strength of hydrodynamic interaction between the near-shore and offshore, the reservoir of phytoplankton available to the mussels is potentially inexhaustible. Only by further reductions in open lake P concentrations can this phytoplankton supply be reduced. Such a reduction would require international action and agreement. Although it may be difficult to bring about local improvement through local reductions in P loading because the mussels are now the dominant source of P loading in the coastal zone, it is possible to make the current situation much worse. Cladophora growth remains under P limitation at depths less than 5-7 m and any significant, persistent increase in local loading of P may lead to much higher production of algal material at all depths where light is not limiting growth. The improved transparency since the early 1990 s in the coastal zone as a result of dreissenid feeding now allows Cladophora to grow to deeper depths and consequently over larger areas. Continued vigilance to keep P loading under control is necessary to avoid aggravation of an already serious problem. Because the rocky substrata and increasing amount of hard substratum provided by dreissenid shell deposits are extensive along the northern coastline of Lake Ontario, the growth of Cladophora is also extensive in area and may be increasing. Coastal currents can detach and transport algal material substantial (but presently unknown) distances. Consequently harvesting of Cladophora to avoid local beach fouling cannot 3

4 be recommended. Further research on Cladophora detachment and transport is required and is underway at Ontario Power Generation s Pickering and Darlington nuclear plants where Cladophora fouling is an operational problem with serious economic consequences. The University of Waterloo is currently developing and validating a linked hydrodynamic-water quality-cladophora growth model for decision support by OPG on how to reduce the risk of algal fouling at the nuclear plants. This model if successfully validated may be of use to OWWRC municipalities in defining future management options. Introduction Through the late 1990 s and into the new century, coastal municipalities and their water utilities along northern and western shores of Lake Ontario from Niagara Region east past the City of Toronto (covering the Golden Horseshoe region of Ontario) received increasing frequency of complaints about fouling of beaches by decaying organic material. This beached rotting material produced a foul odor that discourages people from enjoying the lake front and is so offensive in sight and smell as to be confused with raw sewage. In fact, this material is almost entirely composed of a single filamentous algal species, Cladophora glomerata, that can grow in attached luxuriant stands along rocky shores of the Great Lakes. The alga becomes a nuisance when it grows to high abundance and detaches from its rocky habitat in mid-summer, typically July into August in western Lake Ontario, although shoreline fouling can be observed even into the fall. In response to the concerns of resident rate-payers in municipalities along the coast, members of the Ontario Water Works Research Consortium (OWWRC) asked the Ontario Clean Water Agency (OCWA) to undertake a research programme on the causes and possible control of nuisance algal growth that was causing these beach foulings. In turn, OCWA invited the University of Waterloo that was already conducting Cladophora research on Lake Erie to expand its research into Lake Ontario and to focus research on the issues concerning the OWWRC. A research agreement was reached and the results and conclusions of the research are presented here. The UW research team wishes to thank members of the OWWRC and their representatives for their continuing support and interest in the study expressed at annual meetings and particularly to Mr. Larry Moore, the coordinator for the study, provided by OCWA who kept us on time and budget but also shared his own research experience of historic Cladophora problems in the great lakes. This Summary Report by faculty and and graduate students of the Department of Biology (Cladophora Study Team) to OWWRC covers five years ( ) of studies conducted under a research agreement between OCWA and the University of Waterloo (Appendix 12). In addition to funding from the OCWA agreement, the research team applied for and received funding from the National Science and Engineering Research Council of Canada (NSERC) for two years (2003 and 2004) under NSERC s Industrial Partnerships Program. This grant titled Benthic filamentous green algae in the Great Lakes: Resurgence and remediation allowed the team to investigate the molecular genetics of Cladophora, develop some unique surveying techniques specific to answering research questions related to Cladophora and also to extend our geographic coverage onto Lake Erie and Lake Huron as well as to the eastern end of Lake Ontario. The latter 4

5 grant received excellent in-kind and subsequent post-doctoral fellowship support from Ontario Ministry of the Environment and cooperation from the National Water Research Institute in Burlington Ontario. The results of all the above funded research are reported here when they are relevant to the objectives of the OCWA agreement because the OCWA agreement provided the rationale meeting the criteria for the Partnership Grants program of NSERC. The full final report for the OCWA agreement consists of this summary and 12 appendices. The appendices are: Appendix 1: An Ecological Review of Cladophora in the Laurentian Great Lakes by S. N. Higgins, L. Campbell, V. Hiriart-Baer, S. Y. Malkin, E. T. Howell, S.J Guildford, and R. E. Hecky Appendix 2: Fine scale variation of Cladophora sp. biomass using a novel hydroacoustic mapping method by D. Depew and R. E. Hecky Appendix 3: Organic Tissue Stoichiometry of Cladophora glomerata along the Great Lakes Halton Shoreline by Adam Houben, David Depew, S. J. Guildford, R. E. Hecky Appendix 4. Molecular Systematic Characterization of Cladophora in the Great Lakes by Sarah Ross and Kirsten Muller Appendix 5. Modeling the Growth of Cladophora in the Laurentian Great Lakes in Response to Changes Due to the Exotic Invader Dreissena and to Lake Warming by Sairah Y. Malkin, S. J. Guildford, R. E. Hecky Appendix 6. Phosphorus uptake and release by Cladophora in Lake Ontario by Sairah Malkin and R.E. Hecky Appendix 7. Dreissenid Biomass and Bioavailable Phosphorus Recycling Along the Halton Shore Line of Lake Ontario by Tedy Ozersky and R.E. Hecky Appendix 8. Assessing the Influence of Spatial Heterogeneity of Environmental Parameters on Cladophora growth dynamics in Lake Ontario by S.N. Higgins Appendix 9. Use of pulse amplitude modulated fluorescence to assess light versus nutrient limitation in Cladophora glomerata from Lake Ontario by Véronique P. Hiriart- Baer, Tim J. Arciszewski, Sairah Malkin, S. J. Guildford, R. E. Hecky Appendix 10. Cladophora resurgent and revisited: A brief literature review by V. P. Hiriart-Baer, L. M. Campbell, S. N. Higgins, M. N. Charlton, Laurence F. Moore, S. J. Guildford and R. E. Hecky Appendix 11. Annual Reports: 2003, 2004, 2005 by Cladophora Study Team Appendix 12. The University of Waterloo-OCWA Research Agreement Details of methodologies, data presentation and results and extended discussion of the conclusion of the individual study initiatives is to be found in the appropriate appendices while this summary report highlights the conclusions of all the studies relevant to the five objectives set forth in the research agreement. The appendices will be referenced as appropriate in the Summary Report and also especially illustrative figures or tables will be presented in the Summary Report although they can also be found within the cited appendices. The purpose of the summary report is to inform the interested reader of the major conclusions of the studies relevant to the objectives for the research without having to become familiar with the finer details of the individual studies. Most of the appendices are intended to be published as components of student M.Sc. and 5

6 Ph.D. theses and some have already been submitted to scientific journals for publication in the primary scientific literature. The Cladophora Study Team requests that no portion of the Summary Report or the appendices be reproduced without permission of the appropriate authors or their representative. 6

7 Objectives The OCWA-UW Research Agreement identified five objectives given as stated in the agreement for the funded research. The Summary Report is divided into five sections addressing each of these objectives. These objectives and section headings are: 1. Determine whether periphyton biomass is increasing. 2. Establish the sites of excessive growth of noxious species and, if possible, the specific sites that contribute to on-shore complaints. 3. Investigate the causes of increased biomass and changes in species composition. 4. Determine the impact of local sources of nutrients, including wastewater plants, on biomass production. 5. Advise on possible control methods. I. Determine whether periphyton biomass is increasing. What is periphyton? Periphyton, as used in this report, is a term applied to algae growing on or attached to surfaces. These surfaces can be rock, sand particles, mud surfaces or even other plants. The term benthic algae is sometimes used interchangeably and applies to algae growing on the bottom of lakes or surfaces contiguous with lake bottoms. Most periphyton species are unicellular and microscopic in size and literally invisible to the naked eye. The slippery feel of rock surfaces is due to the covering of the rock surface with microscopic periphyton and the gelatinous material secreted by them to enable their attachment to the rocks. Some periphyton are multicellular and filamentous in structure, growing to macroscopic sizes, e.g. over 1 m in length. So even though individual cells are still nearly microscopic because the cells remain attached to each other they create visible long filaments. Cladophora glomerata is an example of a filamentous green algae (the algal family Chlorophyta are commonly referred to as green algae ). Cladophora glomerata is a filamentous green algae that requires attachment through special holdfast cells to rocky substrata for its growth. It is found in flowing rivers as well as wave swept coastal areas where its ability to maintain its position by adhesion to hard surfaces and to grow upward in the well illuminated shallow waters give it an advantage over microscopic periphyton that are restricted to the bottom of the lake. Cladophora has a branching growth habitat (Fig. 1a) which contributes to its nuisance character as the branching filaments allow it to be knitted into coherent masses (Fig. 1b). Although many species of periphyton occur in Lake Ontario, including other filamentous green algal species such as the common Ulothrix and Spirogyra, our examination of all instances of shoreline or water intake fouling reported to us in Lake Ontario have been attributable to Cladophora. Consequently all our studies have focussed on Cladophora as the only periphyton currently causing aesthetic and fouling problems on Lake Ontario. 7

8 Figure 1. A) Cladophora glomerata and its branching growth habit. B) Underwater view of a coherent detached mass approximately one meter across (photo S. Malkin). a b History of Cladophora in the Great Lakes Cladophora has a long history in the Great Lakes (Table 1), and it is most likely native to the Great Lakes. Starting in the 1930 s there were increasing complaints about fouling problems related to Cladophora. In response to these complaints, research in the 1960 s and 1970 s (Appendices 1 and 11) identified the connection between P enrichment and excessive growth of Cladophora. All plants need light for photosynthesis and require nutrients from their environment to produce tissue (biomass) and they may compete for these resources when these resources become limiting. Previous research and our own studies have confirmed that only the element phosphorus (P) limits the growth of Cladophora in the Great Lakes. Because it is a large alga (termed macroalga) species, Cladophora requires relatively large amounts of P to grow large biomasses that can create nuisance growths and beach foulings. Consequently nuisance growths and beach fouling by Cladophora have historically been associated with excess concentrations of soluble reactive phosphate (SRP; the form of P taken up by plants) attributable to high P loadings associated with human populations and their economic activities. Beginning in the 1970 s under the Great Lakes Water Quality Agreement, Canada and the US committed to reducing P loadings to the Great Lakes. These efforts, especially setting concentration discharge limits on waste water treatment 8

9 plants and removal of P from detergents, resulted in reducing P concentrations to agreed target concentrations in the offshore waters of the Great Lakes (Fig. 2). Although the offshore target concentrations were designed to reduce the abumdance of nuisance algae, it had the effect of reducing near shore concentrations as well (Fig. 3 and Fig. 4). Complaints about Cladophora and associated beach foulings also declined, and studies in the early 1980 s documented a decline in Cladophora abundance in shallow waters (out to 5 m depth) and in tissue P concentrations that determine the rate of Cladophora growth (Fig. 5; Appendix 1). Table 1. Cladophora is native to the Great Lakes, and so there is a long history with it (extracted from Campbell et al unpublished MS) with complaints as early as the 1930 s. E=Erie, H=Huron, M=Michigan, O=Ontario, S=Superior, GL=Great Lakes. Oct 1820 E Earliest known description of nuisance algae fitting description of Cladophora: confervae (filamentous algae) that are washed ashore in times of wind, and emit disagreeable effluvia E, H, M, O Earliest formally published report of C. glomerata in the Great Lakes 1871 S Cladophora spp. on bottom sandy sediments, one site with immense quantities 1933 E, O Start of complaints linked to excessive beachings of Cladophora 1940 E Suitable conditions established for excessive growth of Cladophora in western Erie O Anecdotal evidence of excessive Cladophora growth in Lake Ontario 1960 O, GL Opening of St. Lawrence Seaway to ocean shipping (and to foreign species invasions) , E, O E, O Increase in complaints linked to excessive Cladophora in Lakes Ontario and Erie Initiation of first intensive scientific and ecological studies of this species 1963 GL Abundant Cladophora growth reported at various sites in all Great Lakes 1972 GL Initiation of phosphorus reduction and development of phosphorus loading objectives 1983 O Apparent decline in Cladophora biomass from 1970 s levels, attributed to TP reduction 1990 s GL Establishment of Dreissena species in all Great Lakes Late 90 s E, O Apparent resurgence in nuisance nearshore Cladophora & increase in complaints. 9

10 Figure 2. Spring (April- May) offshore (>20 m station depths) TP concentrations in the epilimnion (0-20m) of Lake Superior (open squares), Lake Huron (closed triangles), Lake Erie (closed circles), and Lake Ontario (closed squares) Data provided by NWRI, Environment Canada. 20 (ug L -1 ) 7 (ug L -1 ) 15 (ug L -1 ) 44 (ug L -1 ) 7 (ug L -1 ) Figure 3. Spring means of soluble reactive phosphorus (April 6 May 10) off Oakville as measured at 1.5m depth from Lake Ontario Nearshore Water Quality Atlas (MOE). 10

11 Oakville Total P (ug L -1 ) Figure 4. Along Oakville shorelines in the vicinity of 16 Mile Creek. Spring total P (all forms of P) concentrations are now well below Soluble Reactive P in the 1970 s. P concentrations near shore are lower in the spring than in the seventies. Figure 5. Cladophora biomass at shallow (0-5m) depths at seven sites spanning the north shore of Lake Ontario Samples were collected from 0.5m (solid bar), 1.5m (grey bar), 3.0m (hatched bar), and 5.0m (open bar) see Appendix 1 for details. 11

12 Has Cladophora biomass increased in recent years? The reduction in shallow water biomass of Cladophora by the 1980 s had the unfortunate effect of reducing monitoring and research effort on this former nuisance to nearly zero. An exhaustive search of the scientific literature (Appendix 11) found very few references in the late 1980 s or 1990 s. Only through our research programme has a systematic effort been made to re-survey those sites in Lake Ontario monitored in the earlier years to determine whether increasing complaints of recent years could be substantiated. The recent surveys (Fig. 5; Appendix 11) do not indicate any increase since the1980 s (when biomasses were greatly reduced from the 1970 s) at shallow water depths. In fact there has been a further decline at the shallowest depths of 0.5 and 1.5 m since the 1980 surveys; however at depths of 5 m or greater (Fig. 5) there has not been significant change since the 1980 s. However, these surveys are restricted to relatively shallow depths, and the response of Cladophora to changing environmental conditions at greater depths cannot be determined. Table 2. Conclusions for Objective 1: Has Cladophora production increased in Lake Ontario? Indirect (Pickering) and anecdotal observations indicate that total Cladophora production may have increased However quantitative measures from surveys indicate that production has decreased at shallower depths. Unfortunately historic surveys are limited to shallow depths (<5 m) so growth at deeper depths cannot be directly compared. Offshore P concentrations have dramatically declined since the 70 s and even since the 80 s and remain low (little historic nearshore data) so P is likely to still be limiting growth when light is available Water transparency has increased and so the area with adequate light to sustain Cladophora growth has increased Modeling is only approach to estimating total production in response to increasing transparency Has the Lake Ontario environment changed? Light transparency limits the depth to which attached plants can grow, including Cladophora (Appendix 1; Appendix 3). Reducing phosphorus concentrations since the 12

13 1970 s did reduce phytoplankton concentrations, and that would have tended to increase light transparency. Light transparency in the near shore is also reduced by turbidity from wave-induced re-suspension of bottom sediments, and runoff from streams and storm sewers. Because of complex nearshore wave dynamics, light conditions can change dramatically both in space and time along coastal environments and this can result in variable growth conditions for Cladophora (Appendices 2 and 8). The same inputs that can degrade light conditions in the near shore can also be relatively rich in P, and so the effect of coastal inflows can be both positive and negative on Cladophora growth rates and biomass. There is evidence from offshore monitoring programmes that light transparency has increased since the 1980 s and especially after the establishment of the invasive dreissenid mussels in the mid-1990 s (Figure 6). Transparency, as measured by the visibility of a white disk (Secchi disk), may have doubled. If this applied equally to the near shore environment, then the amount of bottom area that would receive sufficient light for Cladophora would have also approximately doubled. The internal tissue P concentrations in Cladophora are also a function of light transparency (Appendix 3). At high light intensities, Cladophora growth is saturated with respect to light, allowing growth to proceed rapidly in accordance with its internal P concentration. Through the growing season, as temperatures rise, the rate of Cladophora growth increases. Very early in the season, the growth rate of Cladophora begins to exceed the rate at which it can acquire P, and consequently, measured Cladophora internal tissue P declines through the growing season. Tissue P concentrations measured near the time of maximum biomass (late June-early July in western Lake Ontario), are at their seasonal minimum. At decreasing light intensities at greater depth, Cladophora growth becomes increasingly light limited, and consequently P uptake rate can more closely matche Cladophora rate. At greater depths, during the time of maximum biomass, Cladophora growth becomes light limited and measured internal P concentrations become higher (Appendix 2 and Appendix 5). Internal tissue P concentrations that begin to strongly limit Cladophora growth, approximately 0.2 % P of dry weight, do not occur until 10 m depth in 2006, while in 1972 these concentration occurred at just over 2 m depth (Fig. 7). In this concentration occurred at a depth between these two extremes. Comparing the 1980 s with 2006 indicates that the near shore of Lake Ontario has become more transparent similar to the change inferred from the offshore monitoring station. Our conclusion is that the depth limits of Cladophora growth have increased substantially since the establishment of dreissenid mussels in Lake Ontario. This expansion of habitat can contribute to the total production of Cladophora. However, since the abundance of Cladophora at depths beyond 5 m was not measured in most earlier surveys, direct comparison with earlier estimates is not possible. We have had to model Cladophora growth under scenarios of before and after these changed conditions to quantify the degree of change in Cladophora production attributable to an increasing light environment (section 3 below and Appendix 5). 13

14 8 7 Secchi depth (m) Mar-60 Sep-65 Mar-71 Aug-76 Feb-82 Aug-87 Jan-93 Jul-98 Jan-04 Figure 6. Available data for nearest federal monitoring station to Oakville suggest increase in transparency by a factor of 2 since Note decreasing frequency of observations in summer growing season in the later years. Mussels established in Ontario in early 1990 s. Figure 7. Cladophora growth is light dependent and consequently at maximum biomass, the tissue P concentration, Qp, is depleted at high light and increases as light and growth decreases with depth. So the relationship between Qp and depth is indicative of the transparency of the water. Similar Qp s (red horizontal line) occur at greater depth now compared to earlier years. Transparency in near shore zone has increased two fold since Upper panel shows statistically fitted lines for three different years and the data fitted. Lower panel shows lines extrapolated to common upper value of Qp (0.3 % P of dry matter). QP (% DM) QP (% DM) Depth (m) , Depth (m) 14

15 Lake Ontario is also now on average warmer than it was in the 1980 s and this is a factor that can contribute to the onset of rapid growth and the timing of maximum biomass (Appendices 1, 3 and 5). Mean surface water temperatures (July to September) from Environment Canada monitoring programs have increased by several degrees since 1980 (Fig. 8; Appendix 5). We have evaluated the possible importance of these warmer temperatures to Cladophora growth both historically and the possible effect of even higher temperatures in the future. The effect on the timing of growth increases and the attainment of maximum biomass is affected, but the quantity of Cladophora biomass produced is altered by only a few per cent (Appendix 5). Conclusion for Objective 1: In regards to the first objective of the OCWA agreement we conclude that it is highly probable that Cladophora production has increased along Lake Ontario s northern and western coast since the early 1990 s because of increased light transparency allowing growth to greater depths. Anecdotal observations of shoreline fouling as reported to water utilities have increased. Cooling water intakes have also been clogged with increasing frequency since 2000 as recorded by the amount of Cladophora debris removed from intake screens at the Pickering Nuclear plant. However quantitative measures from surveys indicate that production has decreased at shallower depths (out to three meters depth). Unfortunately historic surveys are limited to shallow depths (<5 m) so growth at deeper depths cannot be directly compared. (low biomass at 5m always measured check. So, don t expect any growth deeper) Offshore P concentrations have dramatically declined since the 70 s and even since the 80 s and remain low. Near shore soluble reactive P concentration measured in April May during the 70 s were much higher than total P measured in a similar period in 2006 which suggests that near shore P concentrations are still quite low compared to historic periods when Cladophora-related complaints were common. Comparison of Cladophora tissue P concentrations at the time of maximum biomass over depth in 2006 indicates very low concentrations and these low tissue P concentrations extend to greater depths now than in the 70 s and 80 s. The greater depth of P deficiency now indicates that water transparency has increased since the 1970 s and 1980 s, and this is consistent with the limited monitoring evidence over that time period. Increasing water transparency has increased the bottom area over which Cladophora can accomplish significant growth and this may have resulted in greater Cladophora production along shorelines with suitable substratum for attachment. However because of the lack of direct observations of Cladophora biomass at depths beyond 5 m, the effect of transparency on the extent of growth can only be quantified indirectly by modeling Cladophora growth. 15

16 Mean Surface Water Temperature ( o C) Year Figure 8. It is getting warmer in Lake Ontario. Upward trend in mean May-August temperatures are evident from Environment Canada measuring station on Lake Ontario. Temperature controls initiation of Cladophora growth in the spring and high mid summer temperatures have been invoked to explain sloughing events. 150 Dry Mass (g/m2) A M J J A S O N Fig. 9. Seasonal cycle of attached Cladophora growth at 2m depth at Oakville in 2004 (a cooler wetter year) and 2005 (a warmer, drier year). From Appendix 5. Establishing sites of growth II. Establish the sites of excessive growth of noxious species and, if possible, the specific sites that contribute to on-shore complaints. 16

17 On-shore complaints On-shore complaints of beached and decomposing Cladophora along the western shorelines of Lake Ontario are most common in mid-summer (July to mid-august) when beaches and shorelines are most visited for recreational purposes. Ontario Power Generation also notes a fall peak in impingement of Cladophora on intake screens at their Pickering Nuclear Plant, but aesthetic complaints may not demonstrate this later movement of Cladophora because there is much less recreational use in the fall and decomposition (and accompanying odours) would be much slower at cooler fall temperatures. The growth cycle of Cladophora (Appendix 1 and 5) in Ontario and Erie consists of a rapid period of growth from late May into late spring-early summer (mid- June) when growth slows and accumulation of attached biomass ceases, after which there is a rapid loss of material from growth sites (Fig. 9; see Fig. 14 for location). This rapid release of plant material is certainly related to the mid-summer termination of growth, senescence and the sloughing of material from growth sites. Between detachment from the growth site and accumulation on a beach, the nearly neutrally buoyant Cladophora strands and larger clumps are subject to transport by coastal currents and wave surges onto beaches or offshore to settle into deeper water. The beached Cladophora may dry and decompose on the beaches or higher waves in subsequent storms may clear the beach. The material transported offshore may settle out onto the bottom in cooler temperatures at intermediate depths beneath the summer thermocline (12-18 m depth; deeper than our survey activities), but this material may not decompose as rapidly as the beached material. The fall peak in Cladophora may be related to breakdown of the thermocline under the cooling temperatures of the autumn and the energetic fall storms that can re-suspend this material off the bottom and enable transport back in shore to cause beach accumulations and fouling of water intakes. Unfortunately little is known about the transport characteristics and fate of detached Cladophora although we may presume that the direction of movement will depend on the variable coastal currents. Consequently, it is currently not possible to traceback an accumulation of beached Cladophora to the site of its growth. Advances in coastal hydrodynamic modeling will be necessary to attempt such tracking. Efforts are ongoing at the University of Waterloo to address this issue with funding from Ontario Power Generation. Previous efforts to measure biomass of Cladophora have required point sampling of locations and depth (at many locations and depths) usually by harvesting plant material from a defined areal quadrat. Even to do such sampling at a coarse spatial interval requires enormous effort and wading, snorkelling or SCUBA diving support. Consequently early survey data are based on a few point samples taken in approximately the same locations and shallow depths (usually less than 3m), and there might only be tens of sampling sites for all of Lake Ontario. Additionally beyond depths of two meters the presence of Cladophora may not be detectable from the surface and so sampling locations were made blindly if not randomly. The challenge of this objective of the study was to develop a new technique that would allow more continuous estimation of Cladophora biomass along significant lengths of shoreline and in the vicinity of known urban inputs that might provide nutrients to fuel Cladophora growth over larger or smaller areas. Such a technique would allow evaluations of the relationships between Cladophora spatial growth patterns to known nutrient inputs and to availability of bottom 17

18 substratum. Furthermore, it could accomplish surveying to greater depths than previous point surveys without the need for SCUBA diving. It would also allow more spatially integrated estimates of the total seasonal accumulation of biomass during the growing season along stretches of shoreline, and thereby put an upper bound estimate on the amount of Cladophora available to foul beaches or water intakes in any particular area. The sampling method chosen was an adaptation of hydroacoustic technology that uses sound transducers and the differential return of an acoustic signal from materials of different densities to estimate presence of plant cover and height over precisely known swaths of bottom area. The hydroacoustic return pings are recorded continuously along with global positioning system (GPS) coordinates to allow mapping of distributions (Appendix 5). The output of the hydroacoustic system allows estimation of bottom type (rock, sand, mud etc.), percentage cover of plant material and plant height from the bottom (Fig. 10). The equipment is mounted on a small craft (Fig. 11) suitable for use in shallow water which is also equipped with sensors to continuously monitor carbon dioxide concentrations and also an underwater video camera to confirm bottom cover and estimate dreissenid mussel (i.e. the zebra mussel Dreissena polymorpha and the quagga mussel D. bugensis) abundances (Appendix 7). In 2005, with funding from NSERC, surveys of Cladophora along shorelines of different land use (predominantly urban, agricultural or forested) and on different lakes were completed in spring and mid summer (Fig. 12). Complaints concerning Cladophora occur on all the lower Great Lakes and the shoreline surveys in 2005 give us a quantitative estimate of the severity of the Cladophora problem in the different lakes and along shorelines with different uses in the same lake. In 2006, repetitive high resolution surveys were done along Halton Region shorelines in the vicinity of Oakville (Fig. 13) to determine if known point sources of nutrient inputs were determining the abundance of Cladophora. Continous hydroacoustic surveys along transects parallel to the shoreline were conducted out to 12 m depths. Water quality (nutrient concentrations, water transparency etc.) and plant tissue chemistry were sampled at fixed stations within the survey area (Fig. 14) along linear transects perpendicular to the shoreline at 2, 5 and 10 m depths to determine how variable growth conditions were along this coast. The Halton shoreline was the focus of the 2006 shorelines because the region had funded a study to quantify nutrient loading by point sources i.e. storm drains, water courses and waste treatment plants along the shoreline (Aquafor Beech Ltd. 2005, Final Report, Conservation Halton, LOSAAC Water Quality Study). This study made it possible to design a survey that would ensure the incorporation of the major point sources on this shoreline. The Aquafor Beech study established that all wastewater treatment plants (WWTP s) together were the largest source of loading followed closely by wet weather loading from watercourses (with largest single nutrient source being 16 Mile Creek) as the dominant sources of nutrients to the Halton coastal waters from land based activities Dry weather loading by the stream courses and then storm sewers accounted for the small remaining fraction of loading. In the coastal area surveyed in 2006 representatives of these major sources of loading are the Oakville Southeast WWTP at the eastern end of the survey area, Sixteen Mile Creek near the center of the area and numerous storm drains scattered along this highly urbanized coastline (Fig. 13 and 14). The WWTP and Sixteen Mile Creek would be similar in their total annual loadings based on the Aquafor Beech Report. Although storm sewers might be rather small loading features along the 18

19 shorelines due to their small discharge, the concentrations of effluent from these sources can be higher than the creeks or the WWTP. In this way, they have the potential to stimulate algal growth locally. However their effect would not be expected to be as spatially extensive as the large loading sources with the their high volume of discharged water. Figure 10. Sample output of hydroacoustic information along a depth transect from 4 to 2 m depth. Upper red line indicates bottom depth and green on top of red indicates plant material (and height). Similar traces below the first return are multiple reflections of the sound signal between water surface and bottom. 19

20 BioSonics DTX unit -430 Khz Khz 6.1 LI-820 IRGA CR10X datalogger Figure 11. University of Waterloo vessel Lady Jane equipped with Biosonics transducer and signal processor and an infrared gas analyzer to estimate CO 2. These systems together with the GPS recorder allow continuous measurement along predetermined transects. Figure 12. Sites of 2005 Great Lakes Surveys of Cladophora cover along shorelines of different land use. 20

21 Figure 13. In 2006 Cladophora surveys were done along Halton region shorelines in the vicinity of Oakville to determine the influence of known point sources on Cladophora growth. WPCC S S 16 Mile Creek 2 m S 602 WTP 601 S WPCC S m (Offshore) Figure 14. Location of water quality sampling stations indicated on a satellite image (Google Map Image) of the Halton shoreline that was surveyed in 2006 for Cladophora growth. WTP water treatment plant, WPCC water pollution contol centres and S indicates storm sewers. Note: Dingle Park is located at site

22 Depth and light controls on Cladophora growth and accumulation Growth of Cladophora is light dependent as in all photosynthetic plants. Therefore the amount of Cladophora growing attached to the bottom of the lake will be strongly dependent on the amount of light reaching the bottom. The amount of light reaching the bottom will depend on the transmission of photosynthetically active light through the overlying waters that in turn is determined by the amount of dissolved colouring material and the amount of suspended material that can absorb or scatter light. Consequently the depth to which Cladophora can grow is dependent on both bottom depth and the transparency of the overlying water. Along Halton shorelines, bottom depth drops off rather rapidly, e.g. compared with Lake Erie, and the 12 m depth contour is approximately parallel to the shoreline (Fig. 15). But there are areas where shallower shelves extend farther offshore. The more extensive the shallow water areas of hard bottom off a length of shoreline the better the light conditions for Cladophora growth if light transimission characteristics of the water column are similar. However, light transmission characteristics are not uniform in coastal areas. This is especially true for suspended materials that can be carried by streams into the coastal areas or where sediments can be resuspended from the bottom during storms. Thus the light environment that bottom dwelling plants experience can be highly variable in time and space along a coast line and this can be difficult to quantify. Cladophora growth though does respond to, and in a sense records, the light environment. At shallower depths, light on the bottom can saturate the photosynthetic system and drive a high nutrient demand to enable growth. At these shallow and/or more transparent locations nutrient availability will determine how much biomass can grow and accumulate. But as depth increases or water clarity is reduced, light will eventually limit the amount of plant growth on the bottom. Cladophora stands can also become self limiting for light, shading its basal cells, in a similar fashion to a forest canopy shading the understory, if large amounts of biomass are able to grow as the overlying plant material absorbs light and limits the amount of light which reaches filaments at the bottom of the stand. If growth is luxuriant, accumulating Cladophora biomass can eventually limit more growth by creating a high demand for nutrients or by imposing light limitation on the accumulating stand of the plant. The top of the plant canopy will have enough light to maintain growth if nutrients are sufficient, but the bottom of the stand will be shaded by the plant material above it. This self-shading will create a metabolic imbalance with respiration for the whole mat exceeding new growth. The Cladophora stand may senesce, and the mat may detach as the basal filaments weaken or die off. But in all cases, the densest stands will be found at shallower depths and biomass will decline at depths beyond which the light transmission properties of the overlying waters limit adequate light penetration to saturate thephotosynthetic potential of the stand. Along Halton shorelines Cladophora growth is strongly light limited beyond 12 m depth and the stand densities become negligible for survey purposes. At the very shallowest depths, generally >1 m depth along exposed Halton shorelines, wave action will also remove a substantive proportion of Cladophora growth and the amount found attached depends both on the growth rate but also the removal rate due to wave driven detachment. Where light availability limits the growth rate of the Cladophora stand, then the filaments will be relatively nutrient, and especially phosphorus, replete (high tissue P 22

23 concentrations). If phosphorus is limiting growth, then tissue P concentrations will become lower and the growth rate of the Cladohora will slow (Fig. 16). By measuring the internal nutrient concentrations of the Cladophora, the degree of nutrient limitation can be assessed. By combining surveys of biomass using hydroacoustic techniques and measuring the internal tissue P concentrations, the effect of local point sources on realized growth or growth potential can be evaluated and sites of excessive or potentially excessive Cladophora growth can be identified as required to fulfill this study objective. Figure 15. Bathymetry of the Halton shoreline surveyed out to 12 m depth. 16 Mile Creek Depth (m) Fig. 16. The relationship between growth potential and internal phosphorus concentrations within Cladophora tissues (Auer and Canale 1982b). ITP concentrations near midummer biomass maximua from Lake Erie (open circle), Lake Ontario (open squares) and Lake Huron (open triangles) from 2006 are reported (Appendix 1). 23

24 Patterns of growth along Halton shorelines As expected, there was a strong relationship between water depth and development of Cladophora cover and biomass along the Halton shoreline. Percent of the bottom covered by Cladophora was between % all along the shore, out to six meters depth beyond which cover dropped as light became strongly limiting (Fig. 17). There was also a tendency for lower coverage by Cladophora at shallowest depths adjacent to the shore compared to depths >2 m although occasionally highest coverage was measured at <2 m depth, e.g. southwest of 16 Mile Creek and approximately 1.5 km northeast of 16 Mile Creek (Fig. 17). This pattern was even clearer in the estimates of biomass with low biomass being found at the shallowest measured depths and again at depths beyond 6-7 m. Where plant coverage was highest immediately adjacent to the shoreline, biomass was also high. The area northwest of 16 Mile Creek was somewhat problematic as video inspections seemed to show that much of the biomass was not attached suggesting that this was an area of accumulation of detached material rather than active growth. Cladophora cover and biomass immediately off the mouth of 16 Mile Creek was low likely as a result of generally high turbidities (low light transparency) and sandy bottom material deposited from the stream. Growth in the immediate vicinity of the Southeast and Southwest WWTP s were not higher than in other parts of the survey area. Percentage cover and biomass were more related to the availability of extensive shallow areas that extended further offshore e.g. where the 6 m contour extended well offshore (green areas in Fig. 15). These are extensive shallow areas are limestone shelves, excellent substratum for Cladophora attachment. Although the areas of high coverage and high biomass in very shallow waters noted above could have storm drains located nearby, there were many cases of storm drains feeding into shallow areas but with only low coverage and biomass The general impression from the hydroacoustic survey at the time of the highest observed biomass was that depth and substratum controlled the distribution and abundance of Cladophora along this shoreline (Table 3). At the peak abundance observed on 22 June 2005 there was approximately 620 tonnes attached Cladophora dry weight in the survey area. One month later over onehalf of this biomass had been removed and only 300 T of biomass expressed as dry weight remained attached (Fig. 19). This amount continued to fall throughout the remainder of the summer into September (Appendix 2). There was no evidence for a second period of high biomass stands in the fall that is sometimes reported in the literature. If the amount of biomass in the survey area were expressed as wet weight of Cladophora and per unit of approximate shoreline length as a straight line from one end of the surveyed area to the other, then the amount of Cladophora potentially available to foul a meter of shoreline can be calculated. By this calculation there would be approximately 600 kg of wet Cladophora per m of shoreline along the 9 km of shoreline surveyed off Oakville at the time of the maximum stand of Cladophora. Of course, not all this material will come up on land, depending on the vagaries of waves and currents; and what does come is not equally distributed along the shoreline. Projections of breakwaters and other structures tend to collect more Cladophora than other reaches but the immensity of the problem is demonstrated by this survey. 24

25 Figure 17. % cover of benthic algae on June Arrow denotes site of localized elevated biomass. Table 3. Cladophora biomass as dry weight at different depths along Oakville shores on 22 June at maximum observed biomass. 620 Tonnes (dry matter or ca T wet weight) for 9 km of shoreline is equivalent to 600 kg wet weight per m of shoreline. Depth Interval (m) Depth (m 2 ) Total Biomass (T) Biomass (g m -2 )

26 Growth of Cladophora along other Great Lakes shorelines Is the Halton Region shoreline at Oakville an area of exceptional growth of Cladophora? The Aquafor Beech report demonstrated that rural catchment areas generated only about one half the loading from the urban catchment areas (excluding the loading from WWTP s). Inclusion of the WWTP s as Urban Loading would suggest that the P loading to Halton regional coastal waters is as much as 4x greater due to urbanization than it would be without urbanization. If such urban loadings lead to higher Cladophora growth, then we might expect that rural shorelines without such adjacent urban centres might have substantially lower Cladophora growth and to be more P deficient in their tissue composition. However, similar hydroacoustic surveys of growth along shorelines at Prequ Ile Provincial Park and at rural shorelines along Lake Erie s eastern basin return similar estimates of Cladophora growth per square meter of the surveyed urban area (Table 4; Appendix 2). In fact the rural shorelines surveyed actually bracketed the values of biomass per square meter in the surveyed areas, and exceeded by a factor of 2 to 3 fold the amount of biomass expressed per unit of shoreline length in the survey areas. The primary determinant of tissue P concentrations for the water quality stations (Fig. 14) off Oakville is sampling depth (which also correlates with light available on the bottom; Fig. 20; Appendix 3), and the concentrations at 2 m depth are similar to concentrations in Erie and Huron (Fig. 16) at peak biomass. The Halton region shore is not an area of excessive Cladophora growth, nor excessively high P concentrations, in Cladophora tissue when compared to other rocky shorelines in the lower Great Lakes. Urbanization is not necessary to generate high biomasses of Cladophora on Great Lakes shorelines. Other factors seem to be more important. Figure 18. Cladophora biomass distribution along Halton shoreline on 22 June Total biomass for surveyed area outlined was 623 T. Arrow denotes area of unusually high biomass 26