D. Q. Kellogg

Coastal Lagoons and Climate Change: Ecological and Social Ramifications in U.S. Atlantic and Gulf Coast Ecosystems

Lagoons are highly productive coastal features that provide a range of natural services that society values. Their setting within the coastal landscape leaves them especially vulnerable to profound physical, ecological, and associated societal disturbance from global climate change. Expected shifts in physical and ecological characteristics range from changes in flushing regime, freshwater inputs, and water chemistry to complete inundation and loss and the concomitant loss of natural and human communities. Therefore, managing coastal lagoons in the context of global climate change is critical. Although management approaches will vary depending on local conditions and cultural norms, all management scenarios will need to be nimble and to make full use of the spectrum of values through which society views these unique ecosystems. We propose that this spectrum includes pragmatic, scholarly, aesthetic, and tacit categories of value. Pragmatic values such as fishery or tourism revenue are most easily quantified and are therefore more likely to be considered in management strategies. In contrast, tacit values such as a sense of place are more difficult to quantify and therefore more likely to be left out of explicit management justifications. However, tacit values are the most influential to stakeholder involvement because they both derive from and shape individual experiences and beliefs. Tacit values underpin all categories of social values that we describe and can be expected to have a strong influence over human behavior. The articulation and inclusion of the full spectrum of values, especially tacit values, will facilitate and support nimble adaptive management of coastal lagoon ecosystems in the context of global climate change.

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.

Nitrous oxide generation, denitrification, and nitrate removal in a seepage wetland intercepting surface and subsurface flows from a grazed dairy catchment

Little is known about seepage wetlands, located within agricultural landscapes, with respect to removing nitrate (NO3 � ) from agricultural catchments, mainly through gaseous emissions of nitrous oxide (N2O) and dinitrogen (N2) via denitrification. These variables were quantified using a push-pull technique where we introduced a subsurface water plume spiked with 15 N-enriched NO3 � and 2 conservative tracers (bromide (Br � ) and sulfur hexafluoride (SF6)) into each of 4 piezometers and extracted the plume from the same piezometers throughout a 48-h period. To minimise advective and dispersive flux, we placed each of these push-pull piezometers within a confined lysimeter (0.5m diameter) installed around undisturbed wetland soil and vegetation. Although minimal dilution of the subsurface water plumes occurred, NO3 � -N concentration dropped sharply in the first 4h following dosing, such that NO3 � -limiting conditions (<2mg/L of NO3-N) for denitrification prevailed over the final 44h of the experiment. Mean subsurface water NO3 � removal rates during non-limiting conditions were 15.7mg/L.day. Denitrification (based on the generation of isotopically enriched N2O plus N2) accounted for only 7% (1.1mg/L.day) of the observed groundwater NO3 � removal, suggesting that other transformation processes, such as plant uptake, were responsible for most of the NO3 � removal. Although considerable increases in 15 N-enriched N2O levelswere initiallyobserved followingNO3 � dosing,no netemissionswere generated over the 48-h study. Our results suggest that this wetland may be a source of N2O emissions when NO3 � concentrations are elevated(non-limited),butcanreadilyremoveN2O(functionasaN2Osink)whenNO3 � levelsarelow.Theseresultsargue for the use of engineered bypass flow designs to regulate NO3 � loading to wetland denitrification buffers during high flow events and thus enhance retention time and the potential for NO3 � -limiting conditions and N2O removal. Although this type of management may reduce the full potential for wetland NO3 � removal, it provides a balance between water quality goals and greenhouse gas emissions. Additional keywords: bromide, denitrification, 15 N, NO3 � removal, N2O, N2, wetland, SF6.

Mineralization of ancient carbon in the subsurface of riparian forests

and 14 C dating of dissolved inorganic carbon revealed that ancient SOC mineralization was common, and that it constituted 31–100% of C mineralization 2.6 m deep at one site, at rates sufficient to influence landscape N budgets. Our data failed to reveal consistent spatial patterns of microbially available ancient C. Although mineralized C age increased with depth at one alluvial site, we observed ancient C metabolism 150 cm deep at a glaciofluvial site, suggesting that subsurface microbial activity in riparian zones does not vary systematically between alluvial and glaciofluvial hydrogeologic settings. These findings underscore the relevance of ancient C to contemporary ecosystem processes and the challenge of using mappable surface features to identify subsurface ecosystem characteristics or riparian zone N-sink strength.

Beaver Ponds: Resurgent Nitrogen Sinks for Rural Watersheds in the Northeastern United States

Beaver-created ponds and dams, on the rise in the northeastern United States, reshape headwater stream networks from extensive, free-flowing reaches to complexes of ponds, wetlands, and connecting streams. We examined seasonal and annual rates of nitrate transformations in three beaver ponds in Rhode Island under enriched nitrate-nitrogen (N) conditions through the use of N mass balance techniques on soil core mesocosm incubations. We recovered approximately 93% of the nitrate N from our mesocosm incubations. Of the added nitrate N, 22 to 39% was transformed during the course of the incubation. Denitrification had the highest rates of transformation (97-236 mg N m d), followed by assimilation into the organic soil N pool (41-93 mg N m d) and ammonium generation (11-14 mg N m d). Our denitrification rates exceeded those in several studies of freshwater ponds and wetlands; however, rates in those ecosystems may have been limited by low concentrations of nitrate. Assuming a density of 0.7 beaver ponds km of catchment area, we estimated that in nitrate-enriched watersheds, beaver pond denitrification can remove approximately 50 to 450 kg nitrate N km catchment area. In rural watersheds of southern New England with high N loading (i.e., 1000 kg km), denitrification from beaver ponds may remove 5 to 45% of watershed nitrate N loading. Beaver ponds represent a relatively new and substantial sink for watershed N if current beaver populations persist.

Modeling the Production of Multiple Ecosystem Services from Agricultural and Forest Landscapes in Rhode Island

This study spatially quantifies hydrological ecosystem services and the production of ecosystem services at the watershed scale. We also investigate the effects of stressors such as land use change, climate change, and choices in land management practices on production of ecosystem services and their values. We demonstrate the approach in the Beaver River watershed in Rhode Island. Our key finding is that choices in land use and land management practices create tradeoffs across multiple ecosystem services and the extent of these tradeoffs depends considerably on the scenarios and ecosystem services being compared.

Modeling anthropogenic nitrogen flow for the Niantic River catchment in coastal New England

ContextThis paper presents a nitrogen flux model that applies previously developed denitrification process equations for an entire catchment. These denitrification equations were previously applied on single flowpaths; this paper implements a model to apply these equations to all possible flowpaths within the catchment.ObjectivesThe purpose of this paper is to describe a new modeling approach (GeoN) to represent and communicate the geospatial interaction between nitrogen sources and sinks within a catchment. This model is of use to local decision-makers because it identifies all areas that are prone to delivering large percentages of nitrogen to sensitive estuaries and those areas that are already providing natural denitrification of the system.MethodsThe GeoN model utilizes a combination of ArcGIS hydrology tools and custom Python scripts to simulate the flow of nitrogen from a source to the catchment outlet. The model also simulates interactions with sinks that provide natural denitrification.ResultsThe model is validated using 11 USGS stream gauge locations. A two one-sided t test (TOST) is performed to evaluate the equivalence between the measured and simulated values. The test shows that the modeled and measured values are not statistically different. The model also simulates overall catchment retention of nitrogen within the range established in the literature for a coastal New England catchment.ConclusionsThis research introduces a model that simulates geospatial interaction of all nitrogen sinks and sources within a catchment allowing the identification of key areas with regards to water quality.

Stream response to an extreme drought-induced defoliation event

We assessed stream ecosystem-level response to a drought-induced defoliation event by gypsy moth caterpillars (Lymantria dispar) with high-frequency water quality sensors. The defoliation event was compared to the prior year of data. Based on long-term records of precipitation and drought indices, the drought of 2015–2016 in Rhode Island, USA was an extreme climatic event that preceded and likely precipitated the defoliation from insect infestation. Canopy cover in the riparian area was reduced by over 50% increasing light availability which warmed the stream and stimulated autotrophic activity. Frass and leaf detritus contributed particulate carbon and organic nutrients to the stream. Based on locally calibrated s::can spectro::lyser data, nitrate concentration and flux did not significantly increase during defoliation while orthophosphate concentration and flux did significantly increase during part of the defoliation period. Lower mean daily dissolved oxygen (DO) levels and wider diel cycles of DO indicated higher biological activity during the defoliation event. Stream metabolism metrics were also significantly higher during defoliation and pointed to heterotrophic activity dominating in the stream. The increases in stream metabolism were low compared to other studies; in streams with higher nutrient levels (e.g., in agricultural or urban watersheds) the increase in light and temperature could have a stronger influence on stream metabolism. The in-stream metabolic processes and nutrient fluxes observed in response to the drought-driven defoliation event resulted from the long-term deployment of high-frequency water sensors. The proliferation of these water sensors now enable studies that assess ecosystem responses to stochastic, unusual disturbances.