An Introduction to The Ecology of Lakes, Ponds and Reservoirs. Developing a Management Plan

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1 An Introduction to The Ecology of Lakes, Ponds and Reservoirs Developing a Management Plan Stephen J. Souza, Ph.D. Princeton Hydro, LLC 1108 Old York Road Ringoes, NJ ssouza@princetonhydro.com

2 Objective of Presentation Introduce standard limnological terms Discuss process of eutrophication Discuss multi-parameter approach to the management and restoration of lakes Introduce importance of management plan Discuss basic elements of a management plan

3 The Need For Lake Management Lakes and ponds susceptible to host of problems that impact water quality, aesthetics, recreational use. Most of these problems are directly linked to the natural process of eutrophication. The eutrophication of lakes, ponds and reservoirs is accelerated by watershed development activities. The most commonly observed symptoms of eutrophication are excessive productivity, sediment infilling, loss of clarity and decline in ecological functions and services.

4 Common Lake Problems

5 What s Eutrophication and Why Should I Care? Increased rate of organic carbon production. Increased primary productivity Primary producers = plants. In lakes = weeds and algae. Result of introducing increasing amounts of nutrients.

6 Eutrophication of Lakes & Ponds Increase in organic carbon translates to more weeds and algae. Phosphorus is the fertilizer of concern...but nitrogen important too! Takes very little phosphorus to stimulate too much productivity 1lb phosphorus can create 1,000 lbs of algae! Most eutrophic lakes need to be on a diet!

7 Eutrophication Oligotrophic Low Productivity Mesotrophic Accelerated by Watershed Development Eutrophic High Productivity

8 Oligotrophic Lake

9 Eutrophic Lake

10 Oligotrophic Vs Eutrophic Water Quality Variable Secchi Depth Clarity Chlorophyll a (mg/m 3) Total Phosphorus (mg/l) EPA Clean Lakes Eutrophic Criteria Average <1m 20 moderate bloom 30 excessive bloom 0.03 enough for bloom, >0.10 hypereutrophic EPA Clean Lakes Oligotrophic Criteria Ave >4 m Less than 2, no significant blooms or less, very little algal productivity

11 Eutrophication Not Linear Productivity Phosphorus Lag effect. Though accelerated by cultural impacts, can take decades to observe. But once tipping point exceeded, changes happen rapidly.

12 Eutrophic Lake - A Not Too Bad

13 Eutrophic Lake - B Not Too Good

14 Don t Just Treat The Symptom Correct the Cause

15 Controlling Eutrophication To successfully identify and address the causes of eutrophication requires... Detailed study of the biological, chemical and physical interactions that define a lake ecosystem. A long-term management plan. Commitment to the plan.

16 Keys To A Successful Plan Clearly defined, realistic goals and objectives. Robust data...foundation of management and restoration decisions. Support...backing of stakeholders. Flexibility...use on-going data collection to objectively assess success of management and restoration efforts; revise management goals and objectives accordingly. Patience...takes time to control eutrophication

17 Lake and Pond Management Plan Flow Chart Data Collection Phase Diagnostic Study Analysis Phase Watershed Mgmt Restoration Action Phase Prevent it! Stop It! Manage it! Fix it! Improve it!

18 Dynamics of Eutrophication Hydrologic Physical

19 Data Collection In-lake data collection In-situ water quality Lab analysis of water samples Biological data Bathymetry Hydrologic data Modeling Watershed loading Hydrology Internal processes Trophic state response Accurate representation Comparable to standards etc Time Consuming Expensive Annual and seasonal variability Saves time Accounts for variability Multi-dimensional Data only as good as model Expensive Must validate

20 Fundamental Lake Interactions Physical Area Depth Shape Size of watershed Thermal properties Chemical Nutrients Dissolved oxygen ph Redox Biological Fish Phytoplankton Macroalgae Zooplankton Hydrologic Inflow Outflow Retention time Flushing Rate

21 Physical Attributes - Morphometry Maximum depth Average depth Must know physical attributes Area of lake/pond Volume Shape of lake Watershed area Watershed area: Lake area ratio Shoreline length

22 Bathymetry - Existing Water Depths

23 Bathymetry - Sediment Thickness

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25 Water Elevation Top of Muck Original Lake Bottom Dredgable Sediment / Added Water Depth

26 Hydrology Extremely important but often overlooked lake attribute Controls rate and amount of external nutrient and sediment loading Affects nutrient assimilation (uptake) Affects mixing, circulation and stratification Water inflow and outflow can be complex Varies seasonally

27 The Importance of Hydrology The more inflow the greater potential for added sediment / nutrient loading But more inflow increases flushing rate This reduces ability for nutrients to be assimilated or sediments to settle.

28 Hydrologic Cycle Water In - Rainfall Runoff Stream baseflow and storm flow Groundwater Permitted discharges Septic systems Water Out - Evaporation Discharge Seepage - gaining Recharge - losing Consumption and use (irrigation, drinking water, etc.)

29 Hydrologic Residence Time Average time to fill lake Affects lake trophic dynamics Can vary seasonally Short res time rapid flow through Long res time - slow flow through Lake Vol (gal) / Outflow Rate (gal/t x ) Very simplified way to compute hydraulic flushing rate

30 Seasonal Effects Note how discharge declines dramatically in summer

31 Impact On Flushing Rate

32 Water Chemistry The water quality of a lake is most accurately defined through the analysis of key parameters Water chemistry varies seasonally affected by Hydrology Water temperature Biological activity Need a technically sound and comprehensive database to truly understand the chemistry of a lake

33 Important Water Quality Parameters ph Alkalinity/Hardness Dissolved oxygen Phosphorus (TP, SRP, DOP, DIP) Nitrogen (NO 3, NH 4 ) Clarity Temperature Chlorophyll a Susp. Sediment Dissolved solids Petro Chemicals Toxins (pesticides) Heavy metals (Cu, Pb) Color (humic acid) E. coli bacteria

34 Phosphorus Loading The more phosphorus, the more algae and weed growth. Phosphorus inputs will vary seasonally and may originate from both internal and external sources. A detailed analysis & quantification of Phosphorus load is the corner stone of a successful diagnostic study.

35 Phosphorus & Nitrogen Sources In-lake (internal) Sediment release and recycling Decomposition of organic material (algae, weeds, fish, etc.) External Stormwater runoff (direct and indirect) Septic systems and wastewater Rainfall Waterfowl

36 Stormwater Sources Residential Road runoff Lawn fertilizer Pet Waste Agricultural Active construction sites Stream bed and bank (erosion)

37 P Loading By Land Use

38 Phosphorus Load By Source Loading Source Load Kg/Yr) % of Total Stormwater (Watershed-Based) % Atmospheric % Septic % Internal regeneration Oxic load % Internal regeneration Anoxic load % Total %

39 Internal Phosphorus Loading Highly affected by Water s thermal properties and stability of water column Oxygen depletion Nutrient and mineral content of sediment

40 Thermal Attributes of Water Its an excellent solvent; many gases, minerals and organics readily are dissolved and are soluble in water. Water has high specific heat, it therefore heats slowly when cold and cools slowly when warm, therefore crating a fairly stable environment.

41 Water s Thermal Properties Temperature/density relationship is unique. Most liquids increase in density as they cool. Water attains maximum density at 4 o C, and then decreases in density as it approaches freezing or becomes warmer than 4 o C. This temperature/density relationship greatly affects the internal mixing properties of lakes, ponds and reservoirs.

42 Thermal Interactions Water column temperature is fairly uniform from surface to bottom Spring Density differences are nominal Lake can freely circulate from top to bottom

43 Thermal Interactions Sun heats upper layers Water temperatures differ from surface to bottom Density differences become significant Thermocline Lake can not freely circulate from top to bottom Summer

44 Thermal Interactions Epiliminion Upper warm layer of lake Metaliminion Transition layer of lake Hypoliminion Deep cold layer of lake Summer

45 Thermal Interactions Water column cool and surface and bottom temperatures are similar Fall Density differences dissipate Lake turns over as it can freely circulate from top to bottom once again

46 Internal Phosphorus Recycling High D.O. Algae Thermocline No D.O. Phosphorus, Fe, SO 4, Mg, Released Sediment Bound Phosphorus, Metals and Minerals

47 Biological Interactions A healthy lake is a complex, biologically balanced ecosystem Phytoplankton and Algae Zooplankton Macrophytes Benthic Invertebrates Vertebrates Decomposers (bacteria) All work together to process and channel energy defines productivity and trophic state

48 Biological Interactions Bottom / Up - Primary producers (weeds and/or algae) exert control over lake conditions Top/Down Consumers (fish) exert control over lake conditions

49 Simoplified Food Web Interactions Phytoplankton Zooplankton Piscivorous Fish Zooplanktivorous Fish Bacteria and Decomposers

50 Classic Top Down Biological Effect A healthy zooplankton community decrease phytoplankton densities via grazing Excessive feeding decreases zooplankton grazing pressure on phytoplankton

51 Weeds and Algae Important, integral part of a lake s ecosystem Base of food chain Source of oxygen Weeds provide habitat for fish and wildlife Weeds help maintain a stable shoreline Weeds can intercept and filter pollutants and sediments Weeds add to the overall aesthetics

52 Alternative Stable States Lakes dominated by either submerged macrophytes (weeds) or by phytoplankton algae. Weed dominated = clear water Algae dominated = turbid water Stable state a function of annual nutrient load. The turbid phytoplankton state tends to exist under high nutrient concentrations, clear water macrophyte state tends to exist under low nutrient concentrations.

53 Summary Lake eutrophication is driven by nutrient loading However, trophic state is defined by various interactions Need to understand all interactions. Physical Hydrological Biological Chemical These data are the foundation of a successful management plan

54 Water Chemistry Is Important, But Hydrology can be a driving factor...often inadequately studied or quantified. Even in relatively shallow lakes, thermal effects can influence productivity and water quality. Biological interactions can greatly alter a lake s water quality top/down and bottom/up effects. Aquatic plants and algae are an important, positive attribute of a healthy lake they need to be controlled but not eradicated.

55 Sources of Information NALMS.ORG NYSFOLA.ORG Diet for Small Lake DEC.NY.GOV CSLAP

56 Thank You

57 Questions. Stephen J. Souza, Ph.D. Princeton Hydro, LLC 1108 Old York Rd., Suite 1 P.O. Box 720 Ringoes, NJ Ssouza@princetonhydro.com