Current projects in the Susquehanna River
The Susquehanna River flows 444 miles from New York to Maryland and is the largest source of freshwater for Chesapeake Bay. The West Branch begins in west-central PA and flows directly past Bucknell University and Lewisburg, PA on its way to join the North Branch 10 miles south of Lewisburg at Sunbury, PA. As a result, the Susquehanna River is an inevitable part of life in central PA, and studies of the Susquehanna River are a natural fit for my research program. Our on-going research in the Susquehanna River includes a variety of projects to study patterns in water quality, benthic community structure and biodiversity, and river metabolism and productivity. In many significant ways, the Susquehanna River valley operates as an integrated riverscape of interactions and exchanges between the land and the river. Humans are an integral part of this riverscape and certainly affect these interactions.

Water quality monitoring (with Ben Hayes and Sean Reese, Bucknell University Environmental Center)
We established real-time continuous water quality monitoring stations in the West Branch Susquehanna River in Milton, PA and in the North Branch Susquehanna River in Danville, PA. These stations have been collecting water quality data from these rivers every 15 minutes and posting it on a website since July 1, 2009 and continue to operate today. High-resolution data generated by these sondes reveal distinct seasonal and flow-related changes in the river and enable us to estimate river metabolism and productivity over long time periods. Information from these stations has been used by staff from Pennsylvania Fish & Boat Commission and Department of Environmental Protection to regulate smallmouth bass fishing and warm-water discharges in the Susquehanna River. Click here for a more extensive description of this monitoring program and access to view the river data.

Metacommunity dynamics of benthic macroinvertebrates (with Matt Wilson, current Master's student)
Metacommunity theory suggests that biological communities interact in ways that influence the taxonomic composition and structure of each other. We are working to understand the linkages among benthic macroinvertebrate communities from different locations and habitats in the Susquehanna River and how these linkages affect community structure in the river and streams across the landscape. River networks link stream and river sites hydrologically and therefore allow movement of organisms by drift or upstream swimming. Streams are also linked by flight of adult aquatic insects and coupled movements with other organisms (e.g., mussel larvae on fish hosts). As a result, benthic communities in streams and rivers are linked to each other through the riverscape of the Susquehanna River. Our studies are beginning by comparing benthic communities from similar habitats in the Susquehanna River to determine if metacommunity processes can help explain spatial patterns within and between riffles. We are also exploring benthic community structure along major tributaries to determine if the Susquehanna River influences communities through mass effects from ovipositing adult aquatic insects or if tributaries influence communities in the Susquehanna River through mass effects of larvae drifting. Future studies will seek to reveal metacommunity processes within the Susquehanna River valey by exploring emergence patterns and movements of adult aquatic insects across the riverscape.

Variability in benthic macroinvertebrate communities (with Matt Wilson, Sean Reese, Mike Bilger, and Ben Hayes)
Many state and federal agencies survey benthic macroinvertebrates as part of routine bioassessment of our nation's water bodies. Data from these collections are rarely used beyond these specific bioassessment programs, but we feel these data could be very useful in providing a source of information about a large number of streams across large areas over long time periods. We collected data from benthic macroinvertebrate surveys conducted by state and federal agencies from the Susquehanna River and major tributaries over a 20-year period (1990-2010) and are analyzing these data to investigate spatial and temporal patterns in benthic macroinvertebrate community structure across the Susquehanna River. Comparing data from multiple agencies over such a long time period proved quite difficult but yielded some very exciting information. Preliminary analyses suggest that benthic macroinvertebrate communities in the river are dominated by mayflies and caddisflies, regardless where you are in the watershed, but that each subbasin (West Branch, North Branch, or main stem) has idiosyncracies in benthic communities. Caddisflies dominated the West Branch but became less significant in downstream sites of the main stem where riffle beetles (esp. Stenelmis) became more abundant. Relative abundance of non-native Asian clams (Corbicula) also increased downstream, indicating its upstream spread from oceans. We also observed inconsistencies between traditional biomonitoring metrics and suggest that alternative metrics or combinations of metrics might be necessary to use benthic macroinverbrate communities for bioassessment of large rivers.

Freshwater mussels (with Sean Reese)
Unionid mussels are native inhabitants of freshwater systems and can be extremely important components of benthic communities. Populations of many freshwater mussels are threatened due to habitat loss from damming in rivers and reductions in populations of host fish (for larval mussels). Unfortunately, like mussel distributions, surveys tend to be patchy due to the difficulty of conducting surveys and increasing lack of expertise to conduct surveys. We have begun surveying mussels in the Susquehanna River and major tributaries to determine current mussel community composition, age structure of different mussel populations, and distributions of mussels in our region. The U.S. Fish & Wildlife Service and U.S. Geologic Survey are partnering to introduce juvenile American eels (Anguilla rostrata) to several tributaries of the Susquehanna River in an effort to restore healthy populations of the Eastern Elliptio (Elliptio complanata). American eels are the preferred host fish for eastern elliptio glochidia, and it is thought that declining eel populations in the Susquehanna River drainage have caused declines in eastern elliptio mussels. Dams in the lower Susquehanna River dramatically reduce the number of American eels migrating into the river as juveniles, and it is hoped that introducing healthy juvenile eels to reaches upstream of the dams will support eel populations and provide hosts for juvenile elliptio mussels. Our monitoring of mussel populations includes streams where eels are being introduced along with several sites in the Susquehanna River to track the success of this eel introduction program and to learn about mussel communities in our region.

Ecosystem metabolism and river productivity
Photosynthesis and respiration by organisms can be measured at the scale of whole ecosystems and are collectively termed "ecosystem metabolism." Metabolism in rivers responds to changes in light, temperature, and flow over daily and seasonal time scales. Daily fluctuations in dissolved oxygen can be quite dramatic if photosynthesis and respiration rates are high and dissolved gases diffuse slowly across the water surface (due to low water velocity). Seasonal In the Susquehanna River, periods of low flow create microhabitats where water is effectively separate from the main flow of the channel, water velocities are very slow, and benthic algae can become very abundant. As a result, these microhabitats have extremely large daily fluctuations in dissolved oxygen, which can be stressful to aquatic organisms. Fluctuations in oxygen may be linked to mortality of juvenile smallmouth bass during low flow years in the Susquehanna River, as these fishes are know to inhabit backwater and river margin microhabitats. We have been studying formation of these microhabitats and development of conditions suitable for severe oxygen fluctuations in the West Branch of the Susquehanna River near Lewisburg. Our research indicates that oxygen stress does not occur in microhabitats during years with above average flow because the river is deep enough to resist oxygen change due to metabolism and because water velocities remain high enough to facilitate gas exchange with the atmosphere, which can offset super-saturated or sub-saturated oxygen concentrations. We would like to model the bathymetry of the Susquehanna River to identify locations where we might expect sensitive microhabitats to exist during low flow. From this, we might be able to target sites that are used by juvenile smallmouth bass and are likely to exhibit stressful oxygen conditions during low-water years to minimize the impact of low flows on this important Susquehanna River sport fishery. Future impacts on river hydrology from climate change and withdrawals for natural gas exploration in Marcellus Shale could exacerbate these flow-dependent ecological conditions, so predicting their occurrence is of interest to federal and state fisheries managers.