Lora A. Harris

Ecological Engineering Practices for the Reduction of Excess Nitrogen in Human-Influenced Landscapes: A Guide for Watershed Managers

Excess nitrogen (N) in freshwater systems, estuaries, and coastal areas has well-documented deleterious effects on ecosystems. Ecological engineering practices (EEPs) may be effective at decreasing nonpoint source N leaching to surface and groundwater. However, few studies have synthesized current knowledge about the functioning principles, performance, and cost of common EEPs used to mitigate N pollution at the watershed scale. Our review describes seven EEPs known to decrease N to help watershed managers select the most effective techniques from among the following approaches: advanced-treatment septic systems, low-impact development (LID) structures, permeable reactive barriers, treatment wetlands, riparian buffers, artificial lakes and reservoirs, and stream restoration. Our results show a broad range of N-removal effectiveness but suggest that all techniques could be optimized for N removal by promoting and sustaining conditions conducive to biological transformations (e.g., denitrification). Generally, N-removal efficiency is particularly affected by hydraulic residence time, organic carbon availability, and establishment of anaerobic conditions. There remains a critical need for systematic empirical studies documenting N-removal efficiency among EEPs and potential environmental and economic tradeoffs associated with the widespread use of these techniques. Under current trajectories of N inputs, land use, and climate change, ecological engineering alone may be insufficient to manage N in many watersheds, suggesting that N-pollution source prevention remains a critical need. Improved understanding of N-removal effectiveness and modeling efforts will be critical in building decision support tools to help guide the selection and application of best EEPs for N management.

Progress and Challenges in Coupled Hydrodynamic-Ecological Estuarine Modeling

Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review, we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a “theory of everything” for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy.

Challenges and Directions for the Advancement of Estuarine Ecosystem Science

Estuarine ecosystem ecology is a dynamic field of study that has historically focused on a spectrum of compelling research topics, and here we present a series of perspectives on the major challenges to be overcome and key research questions to be addressed toward making progress over the coming decades. The challenges we identify include (1) maintaining and improving spatially distributed time-series datasets, (2) maximizing innovation by harnessing new technologies, (3) resuscitating experimental ecosystem research for estuaries, (4) integrating diagnostic ecological models into ecosystem research, and (5) improving basic science by linking it to applied research. We also raise a number of key research questions for the field, including (1) how does food web function respond to changing climate and nutrients, (2) what are likely trajectories of ecosystem recovery in response to restoration, (3) how does climate alter seasonality of estuarine ecosystem processes, (4) how do estuaries affect the global carbon budget and what are key feedbacks, and (5) how will tidal wetland ecosystems respond to sea level rise and climate change? Looking ahead, we envision that the field of estuarine ecosystem ecology will continue to build upon its rich tradition to address fundamental research questions with an expanded toolkit and enlightened perspective to focus basic science on the knowledge needs of society.

Trends in Abundance Indices of Fishes in Maryland’s Coastal Bays During 1972–2009

Maryland’s coastal bays provide habitat for juveniles of many commercially and recreationally important species of shellfish and finfish. Since 1972, the Maryland Department of Natural Resources has conducted the Maryland Coastal Bays Trawl and Seine Survey to monitor the populations of key species. The survey has undergone substantial spatial and methodological changes affecting the interpretation of simple indices of abundance. We developed generalized linear models to standardize the indices of abundance of five commonly caught fish species: Atlantic menhaden Brevoortia tyrannus, weakfish Cynoscion regalis, spot Leiostomus xanthurus, bay anchovy Anchoa mitchilli, and summer flounder Paralichthys dentatus. Density declined significantly since 1972 for menhaden, bay anchovy, and spot in at least one region within the coastal bays. The northern bays had significantly higher densities than the southern bays for all species. Changes in abundance indices of the five species examined were not related to sea grass coverage, temperature, salinity, nitrogen-to-phosphorus ratios, and other habitat variables but were likely a result of stock-wide recruitment processes.

Sediment-Water Nitrogen Exchange along the Potomac River Estuarine Salinity Gradient

ABSTRACT Cornwell, J.C.; Owens, M.S.; Boynton, W.R., and Harris, L.A., 2016. Sediment-water nitrogen exchange along the Potomac River estuarine salinity gradient. Observations of N2 efflux in estuarine sediments across the salinity gradient of the tidal Potomac River, a eutrophic subestuary of the Chesapeake Bay, were used to evaluate environmental controls of microbial denitrification. Rates of denitrification were measured using N2:Ar ratios in core incubations and were similar to other nitrogen-enriched estuaries, with summer and spring N2-N efflux rates averaging 54 ± 47 and 153 ± 97 μmol m−2 h−1, respectively. The paradigm of higher denitrification rates at lower salinities was not supported by observations during summer and spring conditions along this estuarine salinity gradient. Low bottom water oxygen concentrations in the lower, more saline part of the estuary resulted in low rates of coupled nitrification/denitrification. The most favorable region for denitrification in the tidal Potomac River occurred where changes in salinity were most rapid and oxygen concentrations were not depleted, with high rates observed within the estuarine turbidity maximum (ETM) zone. Overall, the key role of salinity in the tidal Potomac River in controlling denitrification appears to be in the focusing of materials into ETM and providing stratification in the lower estuary that restricts the vertical exchange of oxygen necessary for coupled nitrification/denitrification.

Multi-method approach to quantify uncertainties in the measurements of light absorption by particles.

Through technological and research advances, numerous methods and protocols have emerged to estimate spectral absorption of light by particles, ap, in an aquatic medium. However, the level of agreement among measurements remains elusive. We employed a multi-method approach to estimate the measurement precision of measuring optical density of particles on a filter pad using two common spectrophotometric methods, and the determination precision, or uncertainty, of the computational techniques for estimating ap for six ocean color wavelengths (412, 443, 490, 510, 555, 670 nm). The optical densities measured with the two methods exhibited a significant, positive correlation. Optical density measurement precision ranged from 0.061%-63% and exhibited a significant, positive correlation. Multi-method uncertainty ranged from 7.48%-119%. Values of ap at 555 nm and 670 nm exhibited the highest values of uncertainty. Poor performance of modeled ap compared to determined ap suggest uncertainties are propagated into bio-optical algorithms.

Unraveling Phytoplankton Community Dynamics in the Northern Chukchi Sea Under Sea‐Ice‐Covered and Sea‐Ice‐Free Conditions

The timing of sea ice retreat, light availability, and sea surface stratification largely control the phytoplankton community composition in the Chukchi Sea. This region is experiencing a significant warming trend, an overall decrease in sea ice cover, and a documented decline in annual sea ice persistence and thickness over the past several decades. The consequences of earlier seasonal sea ice retreat and a longer sea-ice-free season on phytoplankton community composition warrant investigation. We applied multivariate statistical techniques to elucidate the mechanisms that relate environmental variables to phytoplankton community composition in the Chukchi Sea using data collected during a single field campaign in the summer of 2011. Three phytoplankton groups emerged that were correlated with sea ice, sea surface temperature, nutrients, salinity, and light. Longer ice-free duration in a future Chukchi Sea will result in warmer sea surface temperatures and nutrient depletion, which we conclude will favor other phytoplankton types over larger diatoms. Plain Language Summary In the Chukchi Sea, the seasonality of sea ice shapes ecosystem structure of the water column under both sea-ice-covered and sea-ice-free conditions. As such, phytoplankton community composition under both conditions responds to water column structure and nutrient availability. Owing to recent warming in the Arctic, sea ice is thinner and retreats earlier. To date, we do not fully understand the long-term consequences of earlier sea ice retreat on phytoplankton community composition and carbon biomass. To this end, we used environmental and phytoplankton data to relate how differences in ecosystem function under sea-ice-covered and sea-ice-free conditions govern phytoplankton communities. The results from this data set suggest that a future, sea-ice-free Chukchi Sea will exhibit lower phytoplankton biomass, impacting the food web and carbon export.