Effects of 10 yr of nitrogen and phosphorus fertilization on carbon and nutrient cycling in a tidal freshwater marsh.

Tidal freshwater marshes can protect downstream ecosystems from eutrophication by intercepting excess nutrient loads, but recent studies in salt marshes suggest nutrient loading compromises their structural and functional integrity. Here, we present data on changes in plant biomass, microbial biomass and activity, and soil chemistry from plots in a tidal freshwater marsh on the Altamaha River (GA) fertilized for 10 yr with nitrogen (+N), phosphorus (+P), or nitrogen and phosphorus (+NP). Nitrogen alone doubled aboveground biomass and enhanced microbial activity, specifically rates of potential nitrification, denitrification, and methane production measured in laboratory incubations. Phosphorus alone increased soil P and doubled microbial biomass but did not affect microbial processes. Nitrogen or P alone decreased belowground biomass and soil carbon (C) whereas +NP increased aboveground biomass, microbial biomass and N cycling, and N, P, and C assimilation and burial more than either nutrient alone. Our findings suggest differential nutrient limitation of tidal freshwater macrophytes by N and microbes by P, similar to what has been observed in salt marshes. Macrophytes outcompete microbes for P in response to long-term N and P additions, leading to increased soil C storage through increased inputs of belowground biomass relative to N and P added singly. The susceptibility of tidal freshwater marshes to long-term nutrient enrichment and, hence their ability to mitigate eutrophication will depend on the quantity and relative proportion of N vs. P entering estuaries and tidal wetlands.

Assessing the risk of utilizing tidal coastal wetlands for wastewater management.

Coastal tidal wetlands are well recognized for the key ecosystem services they provide such as flood protection, water quality improvement, and carbon sequestration. In the southeastern United States, some communities rely on coastal wetlands for the management of secondarily treated effluents in forested and emergent wetlands. Advocates for this practice have argued that wetlands can assimilate nitrogen from wastewater, which can improve cypress-tupelo swamp productivity, and enhance marsh accretion rates to mitigate the effects of sea level rise. In contrast, evolving research on coastal wetlands and the environmental impacts of wastewater treatment pose new questions about the potential risks introduced by this practice. This review seeks to: (1) assess current research on plant productivity in fertilized coastal wetlands; (2) highlight the occurrence and fate of pharmaceuticals and personal care products (PPCPs) in municipal wastewater operations; and (3) identify knowledge gaps. Nutrient additions via wastewater augmented aboveground productivity, but decreased belowground productivity and root-to-shoot ratios. Removal efficiencies of some PPCPs by coastal wetlands have been substantial (75% - 99%), but most remain unevaluated. Furthermore, their fate and effect on local ecosystem function and biogeochemical processes remain in question. This review demonstrates that there is more research needed at both local and watershed scales to evaluate how these risk factors impact ecosystem integrity and to better understand the tradeoffs with this wastewater management practice.

Wetland management reduces sediment and nutrient loading to the upper Mississippi river.

Restored riparian wetlands in the Upper Mississippi River basin have potential to remove sediment and nutrients from tributaries before they flow into the Mississippi River. For 3 yr we calculated retention efficiencies of a marsh complex, which consisted of a restored marsh and an adjacent natural marsh that were connected to Halfway Creek, a small tributary of the Mississippi. We measured sediment, N, and P removal through a mass balance budget approach, N removal through denitrification, and N and P removal through mechanical soil excavation. The marsh complex had average retention rates of approximately 30 Mg sediment ha yr, 26 kg total N ha yr, and 20 kg total P ha yr. Water flowed into the restored marsh only during high-discharge events. Although the majority of retention occurred in the natural marsh, portions of the natural marsh were hydrologically disconnected at low discharge due to historical over-bank sedimentation. The natural marsh removed >60% of sediment, >10% of P, and >5% of N loads (except the first year, when it was a N source). The marsh complex was a source of NH and soluble reactive P. The average denitrification rate for the marsh complex was 2.88 mg N m h. Soil excavation removed 3600 Mg of sediment, 5.6 Mg of N, and 2.7 Mg of P from the restored marsh. The marsh complex was effective in removing sediment and nutrients from storm flows; however, retention could be increased if more water was diverted into both restored and natural marshes before entering the river.

Chronic but not acute saltwater intrusion leads to large release of inorganic N in a tidal freshwater marsh.

Sea level rise is expected to increase inundation and saltwater intrusion into many tidal freshwater marshes and forests. Saltwater intrusion may be long-term, as with rising seas, or episodic, as with low river flow or storm surge. We applied continuous (press) and episodic (pulse) treatments of dilute seawater to replicate 2.5 × 2.5 m field plots for three years and measured soil attributes, including soil porewater, oxidation-reduction potential, soil carbon (C), and nitrogen (N) to investigate the effects of continuous and episodic saltwater intrusion and increased inundation on tidal freshwater marsh elemental cycling and soil processes. Continuous additions of dilute seawater resulted in increased porewater chloride, sulfate, sulfide, ammonium, and nitrate concentrations. Plots that received press additions also had lower soil oxidation-reduction potentials beginning in the second year. Episodic additions of dilute seawater during typical low flow conditions (Sept.-Oct.) resulted in transient increases in porewater chloride and sulfate that returned to baseline conditions once dosing ceased. Freshwater additions did not affect porewater inorganic N or soil C or N. Persistent saltwater intrusion in freshwater marshes alters the N cycle by releasing ammonium-N from sorption sites, increasing nitrification and severely reducing N storage in macrophyte biomass. Chronic saltwater intrusion, as is expected with rising seas, is likely to shift tidal freshwater marshes from a sink to a source of N whereas intermittent intrusion from drought may have no long term effect on N cycling.

Differential effects of chronic and acute simulated seawater intrusion on tidal freshwater marsh carbon cycling.

Tidal freshwater ecosystems experience acute seawater intrusion associated with periodic droughts, but are expected to become chronically salinized as sea level rises. Here we report the results from an experimental manipulation in a tidal freshwater Zizaniopsis miliacea marsh on the Altamaha River, GA where diluted seawater was added to replicate marsh plots on either a press (constant) or pulse (2 months per year) basis. We measured changes in porewater chemistry (SO4 2-, Cl-, organic C, inorganic nitrogen and phosphorus), ecosystem CO2 and CH4 exchange, and microbial extracellular enzyme activity. We found that press (chronic) seawater additions increased porewater chloride and sulfate almost immediately, and ammonium and phosphate after 2-4 months. Chronic increases in salinity also decreased net ecosystem exchange, resulting in reduced CO2 and CH4 emissions from press plots. Our pulse treatment, designed to mimic natural salinity incursion in the Altamaha River (September and October), temporarily increased porewater ammonium concentrations but had few lasting effects on porewater chemistry or ecosystem carbon balance. Our findings suggest that long-term, chronic saltwater intrusion will lead to reduced C fixation and the potential for increased nutrient (N, P) export while acute pulses of saltwater will have temporary effects.

Characterizing light attenuation within Northwest Florida Estuaries: Implications for RESTORE Act water quality monitoring.

Water Quality (WQ) condition is based on ecosystem stressor indicators (e.g. water clarity) which are biogeochemically important and critical when considering the Deepwater Horizon oil spill restoration efforts under the 2012 RESTORE Act. Nearly all of the proposed RESTORE projects list restoring WC as a goal, but 90% neglect water clarity. Here, dynamics of optical constituents impacting clarity are presented from a 2009-2011 study within Pensacola, Choctawhatchee, St. Andrew and St. Joseph estuaries (targeted RESTORE sites) in Northwest Florida. Phytoplankton were the smallest contribution to total absorption (at-wPAR) at 412nm (5-11%), whereas colored dissolved organic matter was the largest (61-79%). Estuarine at-wPAR was significantly related to light attenuation (KdPAR), where individual contributors to clarity and the influence of climatic events were discerned. Provided are conversion equations demonstrating interoperability of clarity indicators between traditional State-measured WQ measures (e.g. secchi disc), optical constituents, and even satellite remote sensing for obtaining baseline assessments.

Proof of concept for the use of macroinvertebrates as indicators of polychlorinated biphenyls (PCB) contamination in Lake Hartwell.

The US Environmental Protection Agency (USEPA) develops methods and tools for evaluating risk management strategies for sediments contaminated with polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and other legacy pollutants. Monitored natural recovery is a risk management alternative that relies on existing physical, chemical, and biological processes to contain, destroy, and/or reduce the bioavailability or toxicity of in-place contaminants. These naturally occurring processes are monitored to ensure that management and recovery are progressing as expected. One approach frequently used to evaluate the recovery of contaminated sediments and associated biota is the assessment of contaminant tissue levels, or body burden concentrations, in top trophic level fish. In the present study, aquatic invertebrates were examined as an indicator of recent exposure to PCBs. The approach aimed to determine whether invertebrates collected using artificial substrates (i.e., Hester-Dendy samplers) could be used to discriminate among contaminated sites through the analyses of PCBs in whole homogenates of macroinvertebrates. Macroinvertebrates were sorted, preserved, and analyzed for total PCBs (t-PCBs), by summing 107 PCB congeners. Macroinvertebrate body burden concentrations showed similar trends to sediment t-PCB concentrations at the sites sampled. The results indicate that macroinvertebrates can be used to assess sediment contamination among sites that have different PCB contamination levels.

Application of passive sampling for measuring dissolved concentrations of organic contaminants in the water column at three marine superfund sites.

Currently, there is an effort under way to encourage remedial project managers at contaminated sites to use passive sampling to collect freely dissolved concentrations (Cfree ) of hydrophobic organic contaminants to improve site assessments. The objective of the present study was to evaluate the use of passive sampling for measuring water column Cfree for several hydrophobic organic contaminants at 3 US Environmental Protection Agency Superfund sites. Sites investigated included New Bedford Harbor (New Bedford, MA, USA), Palos Verdes Shelf (Los Angeles, CA, USA), and Naval Station Newport (Newport, RI, USA); and the passive samplers evaluated were polyethylene, polydimethylsiloxane-coated solid-phase microextraction fibers, semipermeable membrane devices, and polyoxymethylene. In general, the different passive samplers demonstrated good agreement, with Cfree values varying by a factor of 2 to 3. Further, at New Bedford Harbor, where conventional water sample concentrations were also measured (i.e., grab samples), passive sampler-based Cfree values agreed within a factor of 2. These findings suggest that all of the samplers were experiencing and measuring similar Cfree during their respective deployments. Also, at New Bedford Harbor, a strong log-linear, correlative, and predictive relationship was found between polyethylene passive sampler accumulation and lipid-normalized blue mussel bioaccumulation of polychlorinated biphenyls (r(2) = 0.92, p < 0.05). The present study demonstrates the utility of passive sampling for generating scientifically accurate water column Cfree values, which is critical for making informed environmental management decisions at contaminated sediment sites.

Risk management of sediment stress: a framework for sediment risk management research.

Research related to the ecological risk management of sediment stress in watersheds is placed under a common conceptual framework in order to help promote the timely advance of decision support methods for aquatic resource managers and watershed-level planning. The proposed risk management research program relies heavily on model development and verification, and should be applied under an adaptive management approach. The framework is centered on using best management practices (BMPs), including eco-restoration. It is designed to encourage the development of numerical representations of the performance of these management options, the integration of this information into sediment transport simulation models that account for uncertainty in both input and output, and would use strategic environmental monitoring to guide sediment-related risk management decisions for mixed land use watersheds. The goal of this project was to provide a sound scientific framework based on recent state of the practice in sediment-related risk assessment and management for research and regulatory activities. As a result, shortcomings in the extant data and measurement and modeling tools were identified that can help determine future research direction. The compilation of information is beneficial to the coordination of related work being conducted within and across entities responsible for managing watershed-scale risks to aquatic ecosystems.