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Ecohydrology modeling to predict effects of environmental change on river inflows and associated ecosystem services in Tillamook Bay, Oregon, USA
Citation:
Marois, D., Ted DeWitt, Bob Mckane, J. Stecher, C. Brown, P. Pettus, AND Pat Clinton. Ecohydrology modeling to predict effects of environmental change on river inflows and associated ecosystem services in Tillamook Bay, Oregon, USA. A Community on Ecosystem Services (ACES) Conference, Washington, DC, December 03 - 06, 2018.
Impact/Purpose:
Estuaries and the coastal watersheds connected to them provide valuable ecosystem services to coastal communities including drinking water, fish and shellfish habitat, and recreation. The provisioning of these services is dependent on the condition of the ecosystems that provide them. By applying the ecohydrology model, VELMA, we are able to predict how the hydrology, water quality, and plant growth of these ecosystems may change in various management and environmental change scenarios. We have parameterized the model using data from the Trask River watershed which borders the Tillamook Bay estuary in Oregon. The Trask River watershed has extensive areas of agriculture, silviculture, and wetland, all of which can be managed by landowners or public agencies in multiple ways. We used measured river flow data and collected water quality samples to calibrate the hydrology and biogeochemical aspects of the model. Running scenarios of different land management strategies within the watershed allows us to predict how they may impact the quantity and quality of river inflows to the estuary. Other future scenarios such as changing wildfire patterns or temperature and precipitation trends have been run to predict what their impact may be. The VELMA model provides results that can be of use to local land managers, fish and wildlife agencies, and programs associated with estuarine health (e.g. the National Estuary Program). This work furthers the goals of the EPA by providing a case study of how a modeling tool can provide beneficial information to community decision-makers in regards to the impacts of watershed management practices on the estuary.
Description:
Estuarine river watersheds provide valuable ecosystem services to their surrounding communities including drinking water and habitat for fish and wildlife; they also affect estuarine water quality. However, the provisioning of these services can be affected by changes in the quantity and quality of river water, such as those caused by altered landscapes or shifting temperature and precipitation trends. We used the ecohydrology model, VELMA, in the Trask River watershed to simulate the effects of environmental change scenarios on estuarine river inputs to the Tillamook Bay (Oregon) estuary. The Trask River watershed is 453 km2 and contains extensive agriculture, silviculture, urban, and wetland areas. VELMA was parameterized using existing spatial datasets of elevation, soil type, land use, air temperature, precipitation and river flow. Water quality samples were gathered in the lowlands and forested areas of the Trask River watershed to calibrate the biogeochemical portion of the model. Hydrology calibrations using USGS river flow data achieved a Nash-Sutcliffe Efficiency of 0.85 for the period of 2007 to 2016. Simulated land use change scenarios include wildfire events and comparisons of varying timber harvest plans. Other scenarios simulated include a 5 ˚C increase in air temperature, which resulted in a 13% decrease in annual flow volume compared to baseline conditions. Our research demonstrates the utility of ecohydrology models such as VELMA to aid in watershed management decision-making. Model outputs of river water flow, temperature, and nutrient concentrations can be linked with other models to predict effects on drinking water quality, salmonid populations, and estuarine water quality. This modeling effort is part of a larger framework of connected models being developed to simulate the networked hydrology and ecology of the estuary, the coastal waters, and the estuarine watersheds. This framework ultimately aims to provide a more complete model of the many factors influencing estuarine ecosystem functions and the services they provide to their associated communities.