Boundary Habitats

2. Boundary Habitats Estuaries

3. Interactions among physical parameters Seasonality

4. Characteristics of biological communities: Marsh habitats • Generally, high density but low diversity • Physiological stresses • Low topographic & substrate variability • But very high potential for productivity due to nutrient input

5. Components • Macrophytes (seagrasses, sedges, rushes, cordgrasses) • Epiphytic algae (macro- and micro-) • Benthic macroalgae and microalgae • Phytoplankton

7. Estuary edge zonation in marshes

8. High primary productivity • E.g., may have >4000 plants per meter square • Second only to tropical rainforests in productivity, among natural ecosystems

9. High secondary productivity • Benthic macrofauna dense • Clams, annelids, crustaceans • Critical for coastal fisheries • Used as nursery areas for many pelagic spp • Approx 2/3 of fishery derived from nursery areas in estuaries • What factors influence this productivity?

10. Questions: • Why are estuaries so productive? • How are offshore fisheries impacted by estuary quality? • What limits productivity? • How are estuaries sensitive to anthropogenic stress?

11. Why are estuaries productive? • Nutrient trap • Tides provide an energy subsidy for the resident aquatic species • Autotrophs are present all year • Combination of freshwater and saltwater creates many different habitats

12. Variety of habitats

13. Physical complexity of an estuary basin Shallow Water Open Water Deep Water Deep Channel A. Cross Section of Chesapeake Bay or Tidal Tributary Migratory Finfish Spawning and Nursery Habitat B. Oblique View of the “Chesapeake Bay” and its Tidal Tributaries Shallow Water Habitat Open Water Habitat DeepWater Deep Channel

14. Freshwater links with estuaries

15. Sediment trapping in tributaries

16. What happens to stream input? • Nutrient (sediment) trap effects due to physical factors • Settling with dispersion of water flow • Nutrients adsorbed on clays • Flocculation • pH & salinity change • alter electrostatic charges • water & small particles attract • increasing particle size and • tendency to settle

17. Biotic sediment trapping: plants Spartina - cordgrass

18. Plant effects in estuarine productivity • Sediment trap effect due to reduction of flow velocity • Nutrient pump effect • Nutrients taken by roots from sediments • Transferred to water column (for phytoplankton) • Nutrient modulation effect • Uptake when nutrients are abundant • Net release back to water when nutrients are scarce (through decomposition)

19. Biotic sediment trapping: animals • Biodeposition • Filter feeders collect suspended matter, compact it • “Clearance rates” can be very high; 10’s of liters per day per clam or oyster

20. Factors enhancing productivity: Tidal mixing • Ebb & flow of tides enhances settling of sediments/nutrients • Resuspension of materials can enhance phytoplankton productivity

21. Factors affecting light & productivity

22. Links between estuaries and fisheries • Fisheries classifications • Economic • Commercial • Recreational • Subsistence • What is being harvested • Arthropods (crabs, shrimp) • Molluscs (clams, oysters) • Fish

23. Offshore fisheries depend on estuaries • 70 – 90% of commercial catch from east coast of USA is estuarine dependent • Fishery productivity is correlated with area of marsh and vegetated habitat

24. Example of fisheries in North Carolina estuaries • Arthropods • Blue crabs ($40 million) • Shrimp ($20 million) • Mollusks • Oysters 1988 peak of $3 million, now <$1 million) • Clams also declining, from 1980 $8 million • Fish • Menhaden, flounder, croaker, weakfish > $24 million • Recreations catch can exceed commercial

25. Estuaries and fisheries, an example

26. Estuaries are especially sensitive to human impacts • Sediment trapping can be problematic • Tradeoff between adding nutrients and increasing turbidity • High sediment loads clog filtering systems of animals • Sediments carry pollutants (dredge spoils of Cape Cod harbors are “toxic wastes”) • Filter feeders tend to concentrate toxins • Estuaries are the “First stop” for poor agriculture and waste management

27. Other reasons for estuarine sensitivity • Vulnerability of estuarine organisms • Many already at the limit of physiological tolerances • Added stress of chemicals, hypoxia may reduce reproduction below critical limits • Food web structure is based on few species • Low diversity is high risk

28. SedimentSources to the Bay and Tribs • Watershed Inputs (1,2 and 3) • Shoreline erosion (4) • Ocean (5) • Biogenic production • Relative contribution varies in proportiondifferent areas of the Bay and tribs

29. Sediment transport in Cheasapeake Bay

30. Sediment Budget – Choptank Estuary 1979-80 (Yarbro et. al, 1983) 12 % Upland 8 % From estuary 80 % Shoreline 81 % Deposited 19 % Transfer downestuary Total Sediment input 0.43 x 106 metric tonnes

31. Why They Are Being Destroyed • Level of habitat loss is ~ 80 to 95% • Many factors contribute to this destruction • Storm sewers are difficult to regulate due to old infastructure (EPA study)

32. Information about Stormwater • More oil than was released in the Exxon Valdez spill flows into Galveston Bay per yr • One quart of spilled motor oil covers three football fields • Takes 20 years for an aquatic system to recover from oil contamination • In the Chesapeake Bay, 15% P, 14% N, and 9% of sediment loads come from storm water

33. Stormwater Pollutants • Suspended soilds from steet dust and eroded sediments • Heavy metals from motor vehicles—wear of plating, bearings and brake linings • Chlorides from salt application • Oils, grease and other hydrocarbons from vehicle exhaust and lubricants

34. Potential PoliciesVegetated Shoreline Buffer Zones • Improve water quality, create new habitat • Difficulties: waterfront land values are expensive, need to remove existing buildings, political opposition, reluctant governments

35. Potential PoliciesBest management practices (BMPs) • Advanced • Detention ponds • Vegetated filter strips • Catch basin filters… • Baseline • Preventive maintenance • Education…. Detention pond