Curtis J. Richardson

Mechanisms Controlling Phosphorus Retention Capacity in Freshwater Wetlands

Freshwater wetland ecosystems do not effectively conserve phosphorus in the way that terrestrial ecosystems do. The phosphorus retention capacity varies greatly among bogs, fens, and swamps and is concomitant with the amorphous acid oxalate-extractable aluminum and iron content in the soil. However, the phosphorus adsorption potential in wetland ecosystems may be predicted solely from the extractable aluminum content of the soil. Wetlands tested as wastewater filtration systems became phosphorus-saturated in a few years, with the export of excessive quantities of phosphate.

Long-term transformation and fate of manufactured ag nanoparticles in a simulated large scale freshwater emergent wetland.

Transformations and long-term fate of engineered nanomaterials must be measured in realistic complex natural systems to accurately assess the risks that they may pose. Here, we determine the long-term behavior of poly(vinylpyrrolidone)-coated silver nanoparticles (AgNPs) in freshwater mesocosms simulating an emergent wetland environment. AgNPs were either applied to the water column or to the terrestrial soils. The distribution of silver among water, solids, and biota, and Ag speciation in soils and sediment was determined 18 months after dosing. Most (70 wt %) of the added Ag resided in the soils and sediments, and largely remained in the compartment in which they were dosed. However, some movement between soil and sediment was observed. Movement of AgNPs from terrestrial soils to sediments was more facile than from sediments to soils, suggesting that erosion and runoff is a potential pathway for AgNPs to enter waterways. The AgNPs in terrestrial soils were transformed to Ag(2)S (~52%), whereas AgNPs in the subaquatic sediment were present as Ag(2)S (55%) and Ag-sulfhydryl compounds (27%). Despite significant sulfidation of the AgNPs, a fraction of the added Ag resided in the terrestrial plant biomass (~3 wt % for the terrestrially dosed mesocosm), and relatively high body burdens of Ag (0.5-3.3 μg Ag/g wet weight) were found in mosquito fish and chironomids in both mesocosms. Thus, Ag from the NPs remained bioavailable even after partial sulfidation and when water column total Ag concentrations are low (<0.002 mg/L).

Processes Controlling Movement, Storage, and Export of Phosphorus in a Fen Peatland

Field and laboratory studies were conducted to determine the mechanisms controlling P movement, storage, and export from a minerotrophic peatland (fen) in central Michigan that had demonstrated high P removal from nutrient additions. An annual P budget completed for the fen ecosystem revealed that plant uptake requirements were 7—9 kg · ha—1 · yr—1, but 35% of aboveground P uptake by plants was returned to the peatland surface via litterfall. Permanent storage of organic P in peat ranged between 2 and 5 kg · ha—1 · yr—1 under natural levels of P input. Both microbial uptake and soil exchange capacity controlled the amount of P made available for plant growth. Fertilizer additions of 5.5 kg · ha—1 · yr—1 of P and 17 kg · ha—1 · yr—1 of N in the fen resulted in no significant (P < .05) increase in growth or nutrient uptake by emergent macrophytes as the litter—microorganism compartment (LMC) retained up to 84% of the added P in year 1. A doubling of the P fertilization level resulted in an LMC retention of ...

Mechanisms controlling soil respiration (CO2 and CH4) in southern peatlands

Abstract Production of soil gases is important in nutrient and carbon cycling, particularly in peatlands due to their large atmospheric emissions of several greenhouse gases. We examined factors controlling aerobic and anaerobic soil respiration in three contrasting types of freshwater North Carolina peatland communities (short pocosins, tall pocosins and gum swamps) which occur along a natural soil nutrient availability gradient. Short pocosins occur in the ombrotrophic center of the bog complexes and are extremely nutrient-deficient; tall pocosins are slightly less nutrient-deficient; and gum swamps are relatively nutrient-rich. Short pocosin had the lowest soil CO 2 production rates under both aerobic and anaerobic conditions in laboratory experiments, while rates in tall pocosin were similar to or somewhat less than in the gum swamp. Methanogenesis rates were extremely low in laboratory experiments, and indicate that CH 4 production is not a significant pathway of carbon flow in these peatlands. Methane production is also low in relation to other peatlands. Amendment experiments indicate that the poor substrate quality of the highly decomposed, humified peat limits both CO 2 and CH 4 production rates, even though the peat is 95% organic matter. Low soil nutrient concentrations and low pH do not directly limit soil respiration in these peatlands, although there is a positive feedback of nutrients with organic matter inputs and litter quality, causing greater soil respiration in nutrient-rich sites. In situ CO 2 emissions similarly differed between the communities, with highest rates in the gum swamp and lowest rates in the pocosins. Emissions were highly seasonal with soil temperature explaining the majority of the temporal variability. Maximum potential CH 4 emission estimates derived from laboratory temperature relationships and in situ soil temperature data indicate that pocosins make an insignificant contribution to the global atmospheric CH 4 flux. The continued existence of peatlands in warm climates may to a large extent depend on the low substrate quality of their soil organic matter, which maintains low decomposition rates under both aerobic and anaerobic conditions.

Environmental and anthropogenic controls over bacterial communities in wetland soils

Soil bacteria regulate wetland biogeochemical processes, yet little is known about controls over their distribution and abundance. Bacteria in North Carolina swamps and bogs differ greatly from Florida Everglades fens, where communities studied were unexpectedly similar along a nutrient enrichment gradient. Bacterial composition and diversity corresponded strongly with soil pH, land use, and restoration status, but less to nutrient concentrations, and not with wetland type or soil carbon. Surprisingly, wetland restoration decreased bacterial diversity, a response opposite to that in terrestrial ecosystems. Community level patterns were underlain by responses of a few taxa, especially the Acidobacteria and Proteobacteria, suggesting promise for bacterial indicators of restoration and trophic status.

Peat Accretion and N, P, and Organic C Accumulation in Nutrient‐Enriched and Unenriched Everglades Peatlands

Recent (1964-1989) rates of peat accretion and nitrogen (N), phosphorus (P), and organic carbon (C) accumulation were measured in Everglades soils to characterize the effects of altered hydroperiod and nutrient regimes on the nutrient storage capacity of the Everglades ecosystem. Peat accretion was related to hydroperiod and phosphorus loading. Accretion rates were highest in areas of extended hydroperiod (2.8-3.2 mm/yr) and/or phosphorus enrichment (4.0 mm/yr) and lowest in areas of reduced hydroperiod (1.6-2.0 mm/yr). Rates of accumulation of nitrogen were 3.8-ll.6 g°m-2 °yr-1 (X = 8.2 g°m-2 ° yr-1 ) and those of organic C were 54-161 g°m-2 °yr-1 (X = 104 g°m-2 °yr-1 ). Accumulation rates of N and organic C were primarily a function of peat accretion rates. Phosphorus accumulation was controlled by both peat accretion and increased soil P content. Soil P concentrations (1248 @m/g) in an area receiving N and P enriched agricultural runoff were 2-3 times higher than P levels at unenriched locations (432-764 mg/g). As a result, rates of P accumulation at this site (0.46 g°m-2 °yr-1 ) were 2-8 times greater compared to unenriched Everglades soils (0.06-0.23 g. m- 2@ ?yr-1 ). Inputs of P (0.53 g. m-2. yr-1 ) and N (15.5 g. m-2 °yr-1 ) to the nutrient-enriched area of Water Conservation Area (WCA) 2A (via rainfall and surface flow) were nine and twelve times higher than inputs to the unenriched part of WCA 2A. As a result, the efficiency of P removal was lower at the enriched site (87%) than at the unenriched location (100%). Nitrogen removal efficiencies also were lower in the enriched area (75%) as compared to the unenriched area, where N accumulation in peat was 290-450% of the input. The difference in N storage efficiencies between the two sites may reflect differences in N fixation and denitrification in nutrient-enriched and unenriched Everglades peatlands. Our findings suggest that nutrient-enriched agricultural drainage has contributed to increased rates of peat accretion and phosphorus accumulation in areas of the northern Everglades that have been receiving agricultural drainage for the past 25-30 yr. The affected area has functioned effectively as a phosphorus sink, primarily due to increased organic P storage. However, the effects of nutrient loading, especially P, on the long-term stability of the Everglades ecosystem and on the long-term P storage potential of Everglades peats are poorly understood and are currently under investigation.

Low Concentrations of Silver Nanoparticles in Biosolids Cause Adverse Ecosystem Responses under Realistic Field Scenario

A large fraction of engineered nanomaterials in consumer and commercial products will reach natural ecosystems. To date, research on the biological impacts of environmental nanomaterial exposures has largely focused on high-concentration exposures in mechanistic lab studies with single strains of model organisms. These results are difficult to extrapolate to ecosystems, where exposures will likely be at low-concentrations and which are inhabited by a diversity of organisms. Here we show adverse responses of plants and microorganisms in a replicated long-term terrestrial mesocosm field experiment following a single low dose of silver nanoparticles (0.14 mg Ag kg−1 soil) applied via a likely route of exposure, sewage biosolid application. While total aboveground plant biomass did not differ between treatments receiving biosolids, one plant species, Microstegium vimeneum, had 32 % less biomass in the Slurry+AgNP treatment relative to the Slurry only treatment. Microorganisms were also affected by AgNP treatment, which gave a significantly different community composition of bacteria in the Slurry+AgNPs as opposed to the Slurry treatment one day after addition as analyzed by T-RFLP analysis of 16S-rRNA genes. After eight days, N2O flux was 4.5 fold higher in the Slurry+AgNPs treatment than the Slurry treatment. After fifty days, community composition and N2O flux of the Slurry+AgNPs treatment converged with the Slurry. However, the soil microbial extracellular enzymes leucine amino peptidase and phosphatase had 52 and 27% lower activities, respectively, while microbial biomass was 35% lower than the Slurry. We also show that the magnitude of these responses was in all cases as large as or larger than the positive control, AgNO3, added at 4-fold the Ag concentration of the silver nanoparticles.

Two statistical methods for the detection of environmental thresholds

A nonparametric method and a Bayesian hierarchical modeling method are proposed in this paper for the detection of environmental thresholds. The nonparametric method is based on the reduction of deviance, while the Bayesian method is based on the change in the response variable distribution parameters. Both methods are tested using macroinvertebrate composition data from a mesocosm experiment conducted in the Everglades wetlands, where phosphorus is the limiting nutrient. Using the percent of phosphorus tolerant species and a dissimilarity index as the response variables, both methods resulted in a similar and well-defined TP concentration threshold, with a distribution function that can be used to determine the probability of exceeding the threshold.

Factors controlling concentration, export, and decomposition of dissolved organic nutrients in the Everglades of Florida

Water draining from the Everglades marshes of southern Florida containshigh concentrations of dissolved organic C (DOC), N (DON), and in somelocations, P (DOP). These dissolved organic nutrients carry over 90% of the Nand organic C, and about 25% of the P exported downstream in the Everglades.Ourobjectives were to describe the most important aspects of the origin and fateofdissolved organic matter (DOM) in the Everglades, and to describe the processescontrolling its concentration and export. Concentrations of dissolved organicnutrients are influenced by local plant production, decomposition, and sorptionequilibrium with peat. The drained peat soils of the Everglades AgriculturalArea and the more productive marshes of the northern Everglades produce some ofthe highest concentrations of DOC and DON in the Everglades watershed. Inportions of the marshes of the northern Everglades, P enrichment was correlatedwith higher local DOC and DON concentrations and greater production of solubleplant matter. Microbial degradation of Everglades DOM was very slow; less than10% of the DOC was lost after 6 months of incubation in the laboratory andsupplements of inorganic nutrients failed to speed the decomposition. Exposureto solar radiation increased the subsequent decay rate of the remaining DOC(25%in 6 mo.). Solar radiation alone mineralized 20.5% of the DOC, 7%of the DON, and degraded about 50% of the humic substances over 21 days insterile porewater samples and thus degraded DOM faster than microbialdegradation. The humic substances appeared to inhibit biodegradation of theother fractions of the DOC since hydrophilic organic acids decomposed fasterwhen isolated from the humic substances.The fate of DOC and DON is closely linked as indicated by a generally narrowrange of C/N ratios. In contrast, high concentrations of DOP were associatedwith P enrichment (at least in pore water). The DOC was composed of about 50%humic substances, 33% hydrophilic acids, and 15% hydrophilic neutralsubstances,typical of DOC from other environments, despite the fact that it originatesfroma neutral to slightly alkaline peatland. Despite high exports of DON (3.9g m−2 y−1 from one area), themarshes of the northern Everglades are a sink for DON on a landscape scale. Theagricultural fields of the Everglades Agricultural Area, however, exported netquantities of DON. High concentrations of DOC desorbed from the agriculturalsoils when water with no DOC was added. Sorption experiments indicated thathighconcentrations of dissolved organic matter flowing into the marshes from theEverglades Agricultural Area could suppress the further desorption ofadditionalsoluble organic matter through physicochemical mechanisms. While biologicalfactors, plant production and microbial decomposition are important inproducingpotentially soluble organic nutrients, physicochemical sorption equilibria,hydrology, and degradation by solar radiation are also likely to control theexport of this material on the landscape scale.

Evaluating Subsampling Approaches and Macroinvertebrate Taxonomic Resolution for Wetland Bioassessment

Methods for wetland bioassessment using macroinvertebrates are not well developed. Two of the most controversial issues in stream bioassessment, subsampling and taxonomic resolution, have yet to be quantitatively addressed for wetlands. Using a multivariate approach, we evaluated the efficacy of family-, genus-, and species-level assemblage data in reflecting the environment and distinguishing impaired sites from the reference condition. We used 5 basic levels of subsampling (100-, 200-, and 300-organism fixed counts; 10% and 25% fixed areas), an integrated subsample requiring a minimum fixed count and fixed area (100&10%), and 100-count and 10%-area subsamples coupled with a supplementary large-rare (LR) search. Data were obtained from 1.5-m2 composite samples collected from 126 plots along a 10-km-long eutrophication gradient in the Florida Everglades. Our results suggest that effectiveness of subsampling depended more upon the minimum number of individuals retained than minimum area or proportion of the sample picked. Fixed-area subsamples were generally less efficient than fixed counts, with 200- and 300-individual fixed counts resulting in significantly greater assemblage-environment relationships and much higher accuracy in detecting impairment than 10% fixed area, despite averaging similar numbers of individuals. The greatest improvement with increasing subsample size was observed between fixed counts of 100 and 200 individuals; detecting impairment, in particular, was not markedly improved with subsample sizes >200 individuals. Supplementing subsamples with a LR search resulted in only very slight improvements in assemblage-environment relationships, but was effective in improving prediction accuracy, particularly for family-level data. However, family-level assemblage-environment relationships and abilities to detect impairment were inferior to genus- and species-level data, regardless of subsample size. Species-level data performed best, primarily because of the large proportion (>20%) of total species belonging to Chironomidae. The potential importance of Chironomidae to wetland bioassessment was further revealed through an evaluation of a tiered-taxonomic approach, which showed that non-Chironomidae family-level data tiered with species-level Chironomidae data produced results very similar to those obtained using genus- or species-level data exclusively. Our results suggest that fixed counts ≥200 or integrated fixed-area/fixed-count approaches that consistently obtain a minimum of 200 individuals should be considered as minimum subsample sizes for wetlands. We additionally advocate LR searches and recommend genus- or species-level taxonomy, particularly for the Chironomidae.