STATEMENT OF EVIDENCE OF Christopher David CORNELISEN

Transcription

1 BEFORE THE BOARD OF INQUIRY IN THE MATTER of the Resource Management Act 1991 AND IN THE MATTER of the Tukituki Catchment Proposal STATEMENT OF EVIDENCE OF Christopher David CORNELISEN Sainsbury Logan & Williams Ref: Lara J Blomfield Solicitors Fax: Cnr Tennyson Street and Cathedral Lane Phone: PO Box 41 Napier

2 CONTENTS 1. Introduction The role of rivers in relation to coastal processes and nutrient loading in coastal waters Existing environment and current conditions in Hawke Bay Forecasted changes in river discharges and nutrient loading likely to occur as a consequence of the RWSS and Change The potential effects of these changes on the coastal receiving environment Recommendations for monitoring Comments on submissions... 9 CDC 1: EXHIBITS Land-use Changes in the Tukituki River Catchment: Assessment of Environmental Effects on Coastal Waters (Cawthron Report 2392 (2013)) Page 2

3 1. INTRODUCTION 1.1 My name is Christopher David Cornelisen. 1.2 I hold a PhD in Marine Biology from the University of South Florida, Tampa, Florida, USA (2003). My doctoral research focused on nutrient dynamics in sub-tropical marine systems. I also hold a MSc in Oceanography from the Florida Institute of Technology, Melbourne, Florida, USA (1996) and a BA in biology from Drake University, Des Moines, Iowa (1991). 1.3 Previously, I have worked for two years as a U.S. National Oceanic and Atmospheric Administration Coastal Management Fellow and for two years as a Postdoctoral Fellow at the University of Otago, where I researched physical and biological processes in New Zealand fiords. 1.4 I am currently employed as a senior scientist at the Cawthron Institute (Cawthron), in Nelson. I have held this position for the last eight years. My work at Cawthron has focused primarily on coastal ecology, coastal water quality, and monitoring of coastal processes. Purpose and scope of evidence 1.5 The purpose of my evidence is to describe the potential effects of land-use changes in the Tukituki River catchment on estuarine and coastal waters in Hawke Bay. 1.6 Specifically, my evidence focusses on the issue of increased nutrient loading on the coastal marine receiving environment and addresses the following matters: (a) (b) (c) (d) The role of rivers in relation to coastal processes and nutrient loading in coastal waters; The existing coastal marine environment and current conditions in Hawke Bay; The forecasted changes in river discharges and nutrient loading that are likely to occur as a consequence of the Ruataniwha Water Storage Scheme (RWSS) and Proposed Plan Change 6 (Change 6); The potential effects of these changes on the coastal marine receiving environment; Page 3

4 (e) Recommendations for monitoring potential effects of increased nutrient loading on coastal water quality seaward of the Tukituki River. 1.7 My evidence provides a summary of the above matters; they are addressed in more detail in my report Land-use Changes in the Tukituki River Catchment: Assessment of Environmental Effects on Coastal Waters (Cawthron Report 2392 (2013)) (Exhibit CDC1). Where I discuss matters that are covered by that report I reference the page number in a footnote. Expert Code of Conduct 1.8 I have read the Code of Conduct for Expert Witnesses in section 5 of the Environment Court s Practice Note (2011). I agree to comply with that Code of Conduct. Except where I state that I am relying upon the specified evidence of another person, my evidence in this statement is within my area of expertise. I have not omitted to consider material facts known to me that might alter or detract from the opinions which I express. 2. THE ROLE OF RIVERS IN RELATION TO COASTAL PROCESSES AND NUTRIENT LOADING IN COASTAL WATERS 2.1 Rivers have a strong influence on coastal processes and are important conduits for the delivery of sediments and nutrients to estuaries and coastal waters. Changes to land-use in a catchment can modify the sediments, nutrients and contaminants carried by rivers into the marine environment, which in turn can lead to changes in marine ecosystems. 2.2 Freshwater from rivers entering coastal water also influences hydrological processes, including the stratification of the water column and estuarine circulation, whereby out-welling river plumes can enhance the input of deep, nutrient-rich oceanic water along the coast. Page 4

5 3. EXISTING ENVIRONMENT AND CURRENT CONDITIONS IN HAWKE BAY 3.1 Hawke Bay is a large coastal water body spanning an area of 2,950 km 2 at high tide 1. Rivers and streams in the Hawke Bay catchments collectively contribute an estimated 6,021 tonnes of nitrogen (N) annually. Of this amount, the Tukituki River contributes about 1330 tonnes total N/year 2. Ultimately, N- loading from rivers will vary considerably depending on rainfall over seasonal, annual and longer time-scales. 3.2 The Tukituki River is the fourth largest river in the region in terms of average flows and the third largest in terms of watershed area. However, it is the region s second largest in terms of annual nitrogen loads, which is a reflection of land-use in the Tukituki River catchment relative to other catchments in the region The Tukituki River flows into a small estuary (0.23 km 2 ) that is well flushed with a very short retention time of 1.2 tidal cycles. As described by Hume (2013) 4, the estuary is essentially an extension of the river that is tidally influenced; its short retention means that the estuary is unlikely to experience adverse effects due to increases in nutrient loading. Hence, the river is effectively a direct conduit for freshwater and associated sediments, nutrients and other materials carried by the river into Hawke Bay. 3.4 Coastal water quality, in terms of trophic conditions, in Hawke Bay varies from oligotrophic (low nutrients and productivity) to mesotrophic (moderately productive). Chlorophyll-a (chl-a) concentrations, a proxy for phytoplankton, are consistent with eutrophic conditions on occasions (particularly during spring) and are higher in deeper waters during summer months. At times nutrients from rivers are likely to contribute to elevated phytoplankton production. This is most likely to occur in late winter through spring months when light levels become less limiting and nutrients are plentiful. 3.5 Time-series data from coastal water quality monitoring conducted by HBRC just north of the Tukituki River mouth indicates N:P ratios typically below an optimal 1 Heath RA, Broad classification of New Zealand inlets with emphasis on residence times. New Zealand Journal of Marine and Freshwater Research 10: Estimates of N loads were obtained from the on-line NIWA Water Resources Explorer model (wrenz.niwa.co.nz/webmodel/). 3 Exhibit CDC1, Figure 4, page Hume T, Key statistics and flushing time for Tukituki Estuary. Letter dated 6 May 2013 provided to Hawke s Bay Regional Council. 2 p. Page 5

6 Redfield ratio of 16:1 5 for marine phytoplankton growth, which suggests that the availability of N is more likely to limit growth of phytoplankton in Hawke Bay than other nutrients. 3.6 This means that if other factors such as light levels are not limiting, increases in N-loading associated with river discharges could enhance growth of phytoplankton and other primary producers such as macroalgae in coastal waters. Additions of other nutrients, such as phosphorous, are less likely to result in increased primary production. 4. FORECASTED CHANGES IN RIVER DISCHARGES AND NUTRIENT LOADING LIKELY TO OCCUR AS A CONSEQUENCE OF THE RWSS AND CHANGE Predicted changes to the Tukituki River flows as a result of implementing the RWSS and Change 6 are both small and in my opinion are likely to have inconsequential effects on the hydrology of the coastal receiving environment. Therefore I do not discuss this further in my evidence. 4.2 Assuming no change in current farming practices, N and P loadings (also referred to as losses from the land) in the Tukituki River are predicted to increase by 30% and 10% across the entire catchment, respectively, as a result of implementing the RWSS and Change If we assume that a 30% increase equates to an equivalent increase in total nitrogen concentrations in the main river near the coast, then the increase in nitrogen loading would equate to an additional ~ 400 tonnes of N on average per year being discharged from the Tukituki River into the coastal receiving environment. 4.4 Placed within the context of Hawke Bay (assuming no changes in the other rivers or outfalls), this increase in nitrogen loads represents an ~ 4% increase in total annual inputs for all rivers and the East Clive and Napier City Council (NCC) wastewater outfalls combined, and an ~ 9% increase for the southern 5 The Redfield ratio can be considered an average for marine phytoplankton. The ratio of C:N:P can vary to some degree depending on location and phytoplankton species. 6 The values of 30% and 10% are revised estimates from Kit Rutherford s evidence that have been provided to me. In Exhibit CDC1, I refer to earlier estimates of 32% and 6% from RWSS Folder 4 Tab 4 Rutherford K Effects of land use on streams Phase 2 modelling studies in the Tukituki River, Hawke s Bay. Prepared for Hawke s Bay Regional Investment Company Limited. NIWA report No: HAM p. My evidence is based on these revised estimates and some statistics such as the estimated increase in total N loading vary slightly from those in Exhibit CDC1. Page 6

7 region that includes inputs from the Tutaekuri / Ngaruroro / Clive, Tukituki and Maraetotara Rivers and the East Clive and NCC wastewater outfalls Nitrate is clearly the dominant form of dissolved inorganic nitrogen in the river, and a 30% increase in nitrogen loading means that a proportional increase in nitrate concentrations is likely to follow. Based on observed concentrations of nitrate in the lower river at Red Bridge 8, a 30% increase in N loading could lead to nitrate concentrations around the recommended median limit of 2.4 mg/l. Depending on the time of the year, rainfall patterns and river flows, the elevated nitrate concentrations in the river could in turn lead to large, periodic increases in the amount of nitrogen being transported within the Tukituki outwelling plume into Hawke Bay. 4.6 A simple model was applied to estimate increases in nitrate concentrations in coastal waters. Model outputs highlighted that the incoming river water will be rapidly diluted as it progressively mixes with the much larger volume of seawater in Hawke Bay, and that increases in nitrogen loading will have the largest effect during winter months when nitrate concentrations are highest and during flood flows when the majority of inputs occur THE POTENTIAL EFFECTS OF THESE CHANGES ON THE COASTAL RECEIVING ENVIRONMENT 5.1 Due to high levels of dilution with seawater, the range of concentrations of nitrate-n in coastal waters are considerably lower (by ~ 10 times 10 ) than those of the Tukituki River and hence the proposal is unlikely to result in nitrate-n concentrations that are considered toxic to marine organisms. 5.2 Increases in nutrient concentrations can lead to eutrophication. An early symptom of eutrophication is increased growth of benthic macroalgae such as sea lettuce (Ulva spp.) that can become a nuisance when abundant. In my opinion, the physical environment (wave action, currents) and habitats adjacent to the Tukituki River mouth (sandy beaches and sandy/gravelly benthos) are unlikely to be conducive to blooms of nuisance macrolagae. 7 Exhibit CDC1, Figure 4, page Change 6, Folder 4, Tab 1, Uytendaal A, Ausseil O Tukituki Catchment: Recommended Water Quality Limits and Targets for the Tukituki Change 6. Resource Management Group Technical Report. EMT 13/04. HBRC Plan No Hawke s Bay Regional Council, Figure 14(A), Page Exhibit CDC1, Figure 9, page Exhibit CDC1, Figure 8, page 18 and Section 5, page 20. Page 7

8 5.3 A more likely effect will be enhanced growth and abundance of phytoplankton in the coastal water column. The magnitude of effects on phytoplankton will depend on a number of factors, including the extent to which nutrient concentrations increase and the amount of light available for photosynthesis (which relates to season as well as water clarity). 5.4 The forecasted increase in nitrogen loading for the Tukituki River represents a small portion of the cumulative loading of nitrogen from multiple rivers, outfalls and (likely much larger) oceanic inputs in Hawke Bay. Consequently, added nutrients from the Tukituki River are more likely to enhance (rather than drive) the growth and abundance of phytoplankton in Hawke Bay. 5.5 Increased nitrate concentrations are most likely to influence important biological processes (phytoplankton production and follow-on food web effects) when the river floods for a prolonged period followed by a period of high light availability. This commonly occurs during late winter to early spring months. 5.6 Biological responses to increased nitrate concentrations, such as an increase in phytoplankton biomass, are unlikely to be immediate. Rather, such responses will be lagged over a period of days to weeks and significantly dampened as the river plume moves offshore and is further diluted with seawater. Furthermore, phytoplankton form the base of the food web, and small increases in phytoplankton can in turn be quickly assimilated into the marine ecosystem. 5.7 Once in the wider marine environment, effects from the incremental increases in nutrient loading from the Tukituki River will be difficult to isolate from changes occurring in response to the cumulative inputs of nutrients from multiple sources. 6. RECOMMENDATIONS FOR MONITORING 6.1 Due to the cumulative nature of land-use effects on downstream marine ecosystems, it is particularly important to maintain long-term datasets that enable the effects of cumulative stressors (including anthropogenic nutrient loading from multiple sources) to be assessed against a backdrop of natural variability. 6.2 I recommend the following in relation to monitoring the effects of increased nutrient loading on the coastal marine receiving environment: Page 8

9 (a) (b) (c) Conduct routine water quality monitoring off the mouth of the Tukituki River that in turn contributes to a wider, long-term coastal monitoring programme for assessing cumulative environmental change in Hawke Bay. Consider application of integrated, multi-parameter indices and analyses of phytoplankton species composition to assess the abundance and frequency of potentially harmful phytoplankton. Implement the use of satellite imagery for monitoring temporal and spatial trends in water quality in the vicinity of the Tukituki River mouth and wider Hawke Bay. 7. COMMENTS ON SUBMISSIONS 7.1 I have been provided with copies of submissions received on Change 6 relevant to the issues I cover in my report and my evidence. 11 In relation to my areas of expertise, these submitters raise concerns about the cumulative effects of landuse (in particular nutrient enrichment effects) on the coastal marine environment. 7.2 I have addressed those matters above and within my report. 7.3 In terms of the matters raised by the submitters, I repeat my conclusion that the predicted increase in nutrient loads that might arise from the implementation of the RWSS, or potentially from the water quality limits set in Change 6, are unlikely to lead to effects beyond small, periodic increases in phytoplankton production. 7.4 Nutrient enrichment in the marine environment falls within the category of cumulative effects since coastal systems such as Hawke Bay are receiving environments for multiple inputs (both anthropogenic and natural) from multiple catchments. Furthermore, other stressors can influence the extent to which increases in nutrients may lead to effects associated with eutrophication Including Quentin Bennett (#99), Operation Patiki (#252, point 6 page 2 and 3), Ngāti Hawea ki Matahiwi Ngāti Kautere, Ngāti Hawea (#379, points 6-8 page 4), Waipatu Marae, Ngāti i Hawea, Ngāti Horea, Ngāti Hinemoa (#395, point 5 page 2), Ngai Te Upokoiri Ki Omahu Marae (#357, points VI page 2 and VIII page 3), and Jenny Baker (#216, page 9), Terry Kelly (# 381) Hawke s Bay and Eastern Fish & Game Councils (#34 and 242), Ngāti Kahungunu Iwi Incorporated (# 51, points page 11), 12 Exhibit CDC1, Figure 9, page 22. Page 9

10 7.5 For these reasons, I have made recommendations that will strengthen and broaden HBRC s coastal monitoring programme and enable the Council to track changes that may be occurring in Hawke Bay over time and in response to a range of drivers including land-use. Signature Chris Cornelisen September 2013 Page 10

11 CDC 1: EXHIBITS Land-use Changes in the Tukituki River Catchment: Assessment of Environmental Effects on Coastal Waters (Cawthron Report 2392 (2013)) Page 11