Estuary Productivity & Complexity Evaluating Human Impacts

Questions: How do people influence estuary productivity? How do people influence estuary productivity? What regulates dynamic processes? What regulates dynamic processes? Which of complex processes are most critical? Which of complex processes are most critical? How do we answer these questions? How do we answer these questions?

Estuaries are especially sensitive to human impacts Sediment trapping can be problematic 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 Estuaries are the “First stop” for poor agriculture and waste management

Other reasons for estuarine sensitivity Vulnerability of estuarine organisms 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 Food web structure is based on few species –Low diversity is high risk

Sediment Sources to the Bay and Tribs Watershed Inputs (1,2 and 3) Watershed Inputs (1,2 and 3) Shoreline erosion (4) Shoreline erosion (4) Ocean (5) Ocean (5) Biogenic production Biogenic production Relative contribution varies in proportion different areas of the Bay and tribs Relative contribution varies in proportion different areas of the Bay and tribs

Sediment transport in Cheasapeake Bay

Sediment Budget – Choptank Estuary (Yarbro et. al, 1983) 12 % Upland 80 % Shoreline 8 % From estuary 81 % Deposited 19 % Transfer down estuary Total Sediment input 0.43 x 10 6 metric tonnes

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

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

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

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

Potential Policies Best management practices (BMPs) Advanced Advanced –Detention ponds –Vegetated filter strips –Catch basin filters… Baseline Baseline –Preventive maintenance –Education…. Detention pond

Systems model approach Start with general, conceptual model Start with general, conceptual model Add specificity and ability to measure Add specificity and ability to measure Evaluate quality and degrees of influence Evaluate quality and degrees of influence Aggregate groups that are very similar; add more specificity where necessary Aggregate groups that are very similar; add more specificity where necessary

Most general level of “model”

2 nd level of abstraction: components Materials to be measured Materials to be measured Processes that define the system Processes that define the system Influences on those processes Influences on those processes Simplify by aggregating functional groups Simplify by aggregating functional groups

Hierarchy, state variables and forces

Vocabulary of systems symbology

3 rd level: Connect the flows, quantify

4 th level: run and evaluate the model

5 th level: refine the model

6 th level: make predictions “What if”... “What if”... Sensitivity analysis Sensitivity analysis

Recent applications

Symbols in model Stressors: sea level rise, societal-driven Stressors: sea level rise, societal-driven Responses: SAV, Oysters, Benthic Diversity, Fish, Manatees, Mangroves Responses: SAV, Oysters, Benthic Diversity, Fish, Manatees, Mangroves Concerns: population declines, loss of habitat, altered hydrology Concerns: population declines, loss of habitat, altered hydrology