Nutrient-enriched Sites Research Articles

A Roman well in Waldgirmes (Hesse, Germany): palynological analyses supported by plant macro-remains and micromorphological studies

Waldgirmes in Hesse (Germany) is one of the oldest Roman towns east of the Rhine River. It was founded in 3 bc and abandoned after ad 9, probably in ad 16, when the departing soldiers set fire to the town. In one of the two excavated wells, partially laminated, organic-rich sediments have been preserved which were deposited during the colonisation of the town. The pollen, plant macro-remains and micromorphological sampling strategy of the well sediment allows us to draw a detailed picture of the vegetation and its development in and around the settlement area. Through thin section analyses, the stratigraphy and composition of sediments could be differentiated in more detail. Deriving from different source areas, the pollen and plant macro-remains assemblages gave insights into the tree species composition of the surroundings as well as the vegetation in the settlement. The town was founded within a cultural landscape that had existed for centuries, and not in the dense dark Germanic forests described by Tacitus around ad 100. The contemporaneous woodlands were dominated by oaks. In the well within the town, not only characteristic components of urban waste (bones, charcoal, ash), but also plant remains from the immediate surroundings (pollen, phytoliths, seeds, fruits, leaves) were preserved. Typical urban vegetation from trodden paths, nutrient-enriched sites, and grazing areas could be reconstructed. Thick leaf layers prove the presence of trees, especially oaks, close to the well. Horticulture is evident through cultural indicators, and there are also signs of cereal processing within the settlement.

Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern California: the Enriched Tree Hypothesis.

The Kuroshio Shot Hole Borer (KSHB, Euwallacea kuroshio) and the Polyphagous Shot Hole Borer (E. whitfordiodendrus; Coleoptera: Curculionidae: Scolytinae) have recently invaded southern California and are attacking live trees in commercial agriculture groves, urban parks and native riparian forests. Among native forests the worst impacts observed to date have been in the Tijuana River Valley in south San Diego County, where approximately 30% of the native willows (Salix spp.), or 120,000 trees, have died as a result of a KSHB infestation. This paper examines wood densities, wood moisture contents, KSHB infestation rates, and KSHB-induced mortality rates in two willow species (Salix lasiolepis and S. gooddingii) at sites near and far from sewage input. Comparisons were made on two spatial scales: broadly among sites within San Diego County; and locally among sites within the Tijuana River Valley. The results showed that, on average, willow trees growing closest to sewage pollution had significantly lower wood density, higher wood moisture content, higher KSHB infestation rates, and higher KSHB-induced willow mortality rates than those growing farther away. We present the Enriched Tree Hypothesis to explain the link between sewage pollution and KSHB impacts; it is as follows: (A) Riparian trees subject to nutrient enrichment from frequent sewage pollution grow quickly, and their fast growth results in wood of low density and high moisture content. If attacked by the KSHB, the trunks and branches of these nutrient-enriched trees provide an environment conducive to the fast growth of the symbiotic fungi upon which the KSHB feeds. With an abundant food supply, the KSHB population increases rapidly and the trees are heavily damaged by thousands of KSHB galleries in their trunks and branches. (B) Riparian trees not subject to frequent sewage pollution grow more slowly and have denser, drier wood. Conditions in their trunks and branches are not conducive to the fast growth of the KSHB’s symbiotic fungi. The KSHB generally ignores, or has low abundances in, these slow-growing trees. This new hypothesis explains current patterns of KSHB impact in San Diego County and focuses attention on the important roles of the environment and preexisting conditions of trees in determining the extent of KSHB impact. It highlights the Tijuana River Valley as an unusual site due to high sewage inputs and predicts that the high KSHB-induced willow mortality seen there should not occur in other natural riparian habitats in southern California. Most importantly, by identifying sewage pollution (or nutrient enrichment) as a major risk factor for KSHB impacts, the hypothesis ratchets down the KSHB-threat level for most riparian sites in southern California and directs attention to other nutrient-enriched sites as those most at risk.

Controls of climate, catchment erosion and biological production on long-term community and functional changes of chironomids in High Arctic lakes (Svalbard)

Arctic freshwater basins are diversity hotspots and sentinels of climate change, but their long-term variability and the environmental variables controlling them are not well defined. We examined four available lake sediment sequences from High Arctic Svalbard for their subfossil Chironomidae communities, biodiversity and functional traits and assessed the influence of climatic and limnological variability on the long-term ecological dynamics. Our results indicated that collector-filterers had an important role in the oligotrophic sites, whereas collector-gatherers dominated the nutrient-enriched sites with significant bird guano inputs. In the oligotrophic sites, benthic production, taxon richness and taxonomic and functional diversity were highest during the early Holocene, when temperatures showed a rapid increase. An increase in subfossil abundance and diversity metrics was also found in recent samples of the oligotrophic sites, but not in the bird-impacted sites, where the trends were decreasing. When partitioning out the environmental forcing on chironomid communities, the influence of climate was significant in all the sites, whereas in-lake production (organic matter) was significant in two of the sites and catchment erosion (magnetic susceptibility) had only minor influence. The findings suggest that major changes in Arctic chironomid assemblages were driven by climate warming with increasing diversity in oligotrophic sites, but deteriorating ecological functions in environmentally stressed sites. We found that although taxonomic and functional diversity were always coupled, taxonomical and functional turnovers were coupled only in the oligotrophic sites suggesting that the ecological functions operated by chironomids in these low-productivity sites may not be as resilient to future environmental change.

Climate and nutrient effects on Arctic wetland plant phenology observed from phenocams

This study explores how climate and nutrients influence productivity of arctic wetland plants. The Green-excess Index (GEI) derived from Red, Green and Blue digital image brightness values from digital repeat photography (a.k.a. phenocams) was used to track the inter-annual variability in seasonal greening and above ground biomass for two dominant aquatic emergent graminoids on the Arctic Coastal Plain of northern Alaska: Carex aquatilis and Arctophila fulva. Four years of seasonal and inter-annual greening trends show strong differences in timing and intensity of greenness among species. Thawing degree-days (TDD, days above 0°C) was a good predictor of GEI in both A. fulva and C. aquatilis. Employing regression tree analyses, we found a greening threshold of 46 TDD for A. fulva, after which GEI increased markedly, while C. aquatilis greened more gradually with a greening mid-point of 31 TDD. Based on long-term climate records and TDD thresholds, greening date has begun 16 thawing degree-days earlier over the past 70years. To understand the effects of latitude and nutrients on seasonal greening, we compared southern sites and nutrient enriched sites with reference sites. We found statistically higher greenness in southern sites and enriched sites compare to reference sites in both plant species, supporting the role of nutrients and warmer temperatures as key factors enhancing productivity in arctic wetlands. In addition, this study provides an inexpensive, alternative method to monitor climate and nutrient effects at high frequency in arctic aquatic systems through camera-derived GEI greenness and has the potential to bridge the gap between plot level and satellite based observations given its strong relationships with biomass and NDVI.

Spatial variation in rates of benthic denitrification and environmental controls in four New Zealand estuaries

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 556:59-77 (2016) - DOI: https://doi.org/10.3354/meps11865 Spatial variation in rates of benthic denitrification and environmental controls in four New Zealand estuaries Catherine Gongol1, Candida Savage1,2,* 1Department of Marine Science, University of Otago, PO Box 56, Dunedin, New Zealand 2Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa *Corresponding author: candida.savage@otago.ac.nz ABSTRACT: Denitrification plays a key role in global biogeochemical cycles as the main nitrogen (N) loss process that limits availability of N to primary producers. This study presents the first measurements of sediment denitrification rates for New Zealand estuaries. Spatially explicit rates of direct denitrification (Dw) and coupled nitrification-denitrification (Dn) were quantified using the isotope pairing method in 4 oligotrophic to moderately nutrient-enriched estuaries on the South Island, New Zealand (Avon-Heathcote, Waikouaiti, Tokomairiro, Tautuku). Coupled nitrification-denitrification dominated (>86%), with most sites having low dissolved inorganic nitrogen (DIN) concentrations (<30 µmol l-1). Rates of total denitrification (Dtot) and Dn were negatively correlated with percent sand and positively related to oxygen penetration depth (OPD). Surface sediment chlorophyll a concentrations and percent carbon (%C) were also identified as significant predictors of Dtot and Dn in the single-factor models. By contrast, Dw was the main nitrogen removal process at moderately nutrient-enriched sites and was positively related to DIN concentrations in the water column and negatively correlated with percent sand. OPD and %C were also identified as significant predictors of Dw. While Dw was positively related to DIN concentrations, overall rates of denitrification were not, demonstrating that predictive relationships between N loading and removal are not always possible in oligotrophic estuaries. Our findings demonstrate the importance of grain size as a driver of denitrification rates in estuaries and imply that an increase in fine-grained sediments from land-use intensification may alter rates of N removal in estuaries through complex direct and indirect processes. KEY WORDS: Denitrification · Estuaries · New Zealand · Nitrogen · Benthic · Sediment grain size · Isotope pairing method · Oxygen flux Full text in pdf format PreviousNextCite this article as: Gongol C, Savage C, (2016) Spatial variation in rates of benthic denitrification and environmental controls in four New Zealand estuaries. Mar Ecol Prog Ser 556:59-77. https://doi.org/10.3354/meps11865 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 556. Online publication date: September 08, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Factors affecting spatiotemporal benthic macroinvertebrate diversity and secondary production in a semi-arid watershed

Spatial and temporal changes of the benthic macroinvertebrate (BMI) community composition and secondary production provide valuable information about the current ‘health’ of aquatic systems. We analyzed seasonal and inter-annual changes in BMI communities at five sites along an elevation and land use gradient in the Walker River, NV, USA. In addition, bimonthly collections of Baetis mayflies were made at two sites to assess the effect of nutrient enrichment on Baetis secondary production. BMI community composition changed spatially and temporally in response to the physicochemical environment. BMI diversity was positively correlated to substrate size and stream width but negatively correlated with stream temperature and organic pollutants. Cluster analysis based on BMI community composition revealed a similar community structure along the river, except at one site which was located below the outflow of a eutrophic reservoir. The BMI community in the river was dominated by collector–gatherers while shredders were absent through most of the downstream and impaired sites. Secondary production of Baetis was almost twice as high at the nutrient-enriched site (1.3 g dry mass m−2 yr−1) than at the undisturbed site (0.7 g m−2 yr−1), most likely the consequence of warmer water temperatures and superior food quality. Results from this study imply that a variety of anthropogenic activities have altered disparate reaches of the Walker River and that BMI community composition would change towards natural conditions with an increase in discharge and reduced water temperature and nutrients. This work also underscores the importance of considering biotic indices and secondary production to effectively assess stream ecosystem health and to design successful restoration strategies.

The use of the brown macroalgae, Sargassum flavicans, as a potential bioindicator of industrial nutrient enrichment

Nutrient bioindicators are increasingly being recognised as a diagnostic tool for nutrient enrichment of estuarine and marine ecosystems. Few studies, however, have focused on field translocation of bioindicator organisms to detect nutrient discharge from industrial waste. The brown macroalgae, Sargassum flavicans, was investigated as a potential bioindicator of nutrient-enriched industrial effluent originating from a nickel refinery in tropical north-eastern Australia. S. flavicans was translocated to a number of nutrient enriched creek and oceanic sites over two seasons and assessed for changes in stable isotope ratios of 15N and 13C within the plant tissue in comparison to reference sites. Nutrient uptake in macroalgae, translocated to the nutrient enriched sites adjacent to the refinery, increased 3–4-fold in δ15N, compared to reference sites. Using δ15N of translocated S. flavicans proved to be a successful method for monitoring time-integrated uptake of nitrogen, given the current lack of passive sampler technology for nutrient monitoring.

Trophic responses to nutrient enrichment in a temperate seagrass food chain

Simple ecological models that predict trophic responses to bottom-up forcing are valuable tools for ecosystem managers. Traditionally, theoretical ecologists have used resource-dependent functional responses to explain the modification of food chains exposed to bottom-up perturbations. These models predict alternating positive, negative and zero responses at each trophic level. More recently, ratio-dependent functional response models that predict proportional increases at each level have challenged this paradigm. The present study tested the predictions of the 2 hypotheses empirically by comparing the relative biomasses of 4 trophic levels of an estuarine seagrass food chain in relatively undisturbed, low-nutrient catchments and 'developed' catchments subjected to a prolonged period of nutrient enrichment. We found that nutrient-enriched sites had significantly greater biomass of both epiphytic algae and grazing invertebrates; however, the bottom-up forcing of nutrients was attenuated at higher trophic levels (occupied by juvenile and piscivorous fish), with no significant effect of catchment development. This disconnect in the upward cascade of energy may be due to a number of possible reasons including high levels of diversity and omnivory, trophic subsidy within the system or the strength or nature of perturbations. Although the predictions of both hypotheses failed to hold across all trophic groups, ratio dependence was prevalent at the lower levels of the food chain, which has implications for catchment management.

Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river

1. Algal growth in lotic systems is controlled either from the bottom-up (e.g. nutrients and light, which determine growth rates) or from the top-down (e.g. grazing pressure, which reduces accumulated biomass). Nutrient-enriched streams that support large and diverse grazing macroinvertebrate populations and those with shaded riparian corridors rarely suffer from excessive algal growth. 2. In this study, the density of benthic algivorous macroinvertebrates was experimentally manipulated in shaded and open nutrient-enriched stream habitats of the Owennagearagh River, south-west Ireland. The ability of macroinvertebrate grazers and riparian shade to control benthic algal growth [particularly the nuisance alga, Cladophora glomerata (L. Kütz)] was investigated. Three sites with markedly different concentrations of plant nutrients (one site upstream and two sites downstream of the sewage outfall) were selected. The density of grazing invertebrates colonising ceramic tiles was reduced using high-voltage localised electric pulses. Replicates of treatment (grazer-excluded) and control (grazed) tiles were deployed in open and shaded (<25 and >80% canopy cover, respectively) patches of stream bed, in each site. 3. After 2-week Cladophora cover, periphytic chlorophyll a and biofilm ash-free dry mass (AFDM) were quantified for all experimental tiles. Values for all three parameters were highest on grazer-excluded tiles from open patches. Grazed tiles from open patches accrued little Cladophora and had significantly lower levels of chlorophyll a and AFDM. Nutrient inputs were found to have an impact on the density of grazing invertebrates, with higher densities of Baetis nymphs at the most nutrient-enriched site. 4. Our results demonstrate that in eutrophic, high-light streams, filamentous algae can quickly accumulate to nuisance levels in the absence of invertebrate grazers. In future, greater attention should be paid to the role of grazing invertebrates in controlling nuisance algae in streams, in addition to algal–nutrient relationships.

Influence of drought and total phosphorus on diel pH in wadeable streams: Implications for ecological risk assessment of ionizable contaminants

Climatological influences on site-specific ecohydrology are particularly germane in semiarid regions where instream flows are strongly influenced by effluent discharges. Because many traditional and emerging aquatic contaminants, such as pharmaceuticals, are ionizable, we examined diel surface water pH patterns (i.e., change in pH over a 24-h period) at 23 wadeable streams in central Texas, USA, representing a gradient of nutrient enrichment during consecutive summers of 2006 and 2007. The years of our study were characterized by decidedly different instream flows, which likely affected production:respiration dynamics and led to distinctions in diel pH patterns between 2006 and 2007. Site-specific ambient water quality criteria for NH(3) and the aquatic toxicity of the model weak base pharmaceutical sertraline were predicted using continuous water quality monitoring data from the sites. Drought conditions of 2006 significantly increased (p<0.05) diel pH changes compared to high instream flows of 2007,and the magnitude of diel pH variability was most pronounced at nutrient-enriched sites in 2006. Differences in diel pH change patterns between 2006 and 2007 affected predictions of the environmental fate and effects for model weak base pharmaceuticals and NH(3). Overall, site-specific diel pH was more variable at some sites than the difference in mean surface water pH between the 2 summers. Diel pH variability affected regulatory criteria, because 20% of the study sites in 2006 experienced greater than 5-fold differences in National Ambient Water Quality Criteria for NH(3) over 24-h periods. Our study emphasizes the potential uncertainty that diel pH variability may introduce in site-specific assessments and provides recommendations for environmental assessment of ionizable contaminants.

After the fence: vegetation and topsoil condition in grazed, fenced and benchmark eucalypt woodlands of fragmented agricultural landscapes

Emerging ecological theory predicts that vegetation changes caused by introduction of livestock grazing may be irreversible after livestock are removed, especially in regions such as Australia that have a short evolutionary exposure to ungulate grazing. Despite this, fencing to exclude livestock grazing is the major tool used to restore vegetation in Australian agricultural landscapes. To characterise site-scale benefits and limitations of livestock exclusion for enhancing biodiversity in forb-rich York gum (Eucalyptus loxophleba Benth. subsp. loxophleba)–jam (Acacia acuminata Benth.) woodlands, we compared 29 fenced woodlands with 29 adjacent grazed woodlands and 11 little-grazed ‘benchmark’ woodlands in the Western Australian wheatbelt. We explored the following two hypotheses: (1) fencing to exclude livestock facilitates recovery of grazed woodlands towards benchmark conditions, and (2) without additional interventions after fencing, complete recovery of grazed woodlands to benchmark conditions is constrained by ecological or other limits. Our first hypothesis was supported for vegetation parameters, with fenced woodlands being more similar to benchmark woodlands in tree recruitment, exotic plant cover, native plant cover, native plant richness and plant species composition than were grazed woodlands. Further, exotic cover decreased and frequency of jam increased with time-since-fencing (2–22 years). However, we found no evidence that fencing led to decline in topsoil nutrient concentrations towards concentrations at benchmark sites. Our second hypothesis was also supported, with higher topsoil nutrient concentrations and exotic plant cover, and lower native plant richness in fenced than in benchmark woodlands, and different plant species composition between fenced and benchmark woodlands. Regression analyses suggested that recovery of native species richness is constrained by exotic species that persist after fencing, which in turn are more persistent at higher topsoil nutrient concentrations. We conclude that fencing to exclude livestock grazing can be valuable for biodiversity conservation. However, consistent with ecological theory, additional interventions are likely to be necessary to achieve some conservation goals or to promote recovery at nutrient-enriched sites.

Phosphorus Transformations during Decomposition of Wetland Macrophytes

The microbially mediated transformation of detrital P entering wetlands has important implications for the cycling and long-term sequestration of P in wetland soils. We investigated changes in P forms in sawgrass (Cladium jamaicense Crantz) and cattail (Typha domingensis Pers.) leaf litter during 15 months of decomposition at two sites of markedly different nutrient status within a hard-water subtropical wetland (Water Conservation Area 2A, Florida). Leaf litter decomposition at the nutrient enriched site resulted in net sequestration of P from the environment in forms characteristic of microbial cells (i.e., phosphodiesters and pyrophosphate). In contrast, low P concentrations at the unenriched site resulted in little or no net sequestration of P, with changes in P forms limited to the loss of compounds present in the initial leaf litter. We conclude that under nutrient-rich conditions, P sequestration occurs through the accumulation of microbially derived compounds and the presumed concentration of endogenous macrophyte P. Under nutrient-poor conditions, standing P pools within wetland soils appear to be independent of the heterotrophic decomposition of macrophyte leaf litter. These conclusions have important implications for our ability to predict the nature, stability, and rates of P sequestration in wetlands in response to changes in nutrient loading.

The collapse of benthic macroalgal blooms in response to self‐shading

Summary1. Our goal was to use physiological indicators [photosynthesis–irradiance (P–I) response, nutrient status], population level feedbacks (self‐shading) and ambient environmental conditions (dissolved nutrients, light, temperature) to improve our understanding of the seasonal and spatial population dynamics ofCladophora.2. Cladophoragrew in three distinct phases, rapid growth early in the season (May–July), a mid‐season population collapse (July–August) and autumn re‐growth. Across all sites and dates, mean net maximal photosynthesis [PM(NET)] was 6.9 ± 3.9 mg O2 g DM−1 h−1, and α was 0.055 ± 0.025 mg O2 g DM−1 μmphotons−1 m−2. Mean values for critical irradiance (ICR) and the half‐saturation light intensity (IK), were 42.9 ± 32.1 and 189.3 ± 123.8 μmphotons−1 m−2 s−1respectively.3. At most sites growth was phosphorus‐limited. Values of α were significantly higher at a site influenced by a nutrient enriched river plume, where algal growth was phosphorus‐sufficient.4. Photoinhibition was not apparent in any of our P–I experiments. Even if photoinhibition had been apparent duringin vitroP–I experiments, population level photosynthetic rates in the field would be little affected because intense self‐shading restricts inhibiting irradiances to the upper few mm–cm of the algal canopy.5. Our physiological (P–I response) experiments contradicted previous assertions that high ambient temperatures, or nutrient deficiency, were primary causes of mid‐summer sloughing. In our study, sloughing occurred simultaneously at nutrient enriched and nutrient deficient sites, at temperatures well below critical values found duringin vitroexperiments, and our indicator of physiological condition (P–I response) remained unchanged leading up to, or immediately after, the sloughing event.6. Self‐shading can reduce the convexity of the P–I response withinin vitroincubations, even when the amount of algal material is low. Our experiments used 0.08 g DM of algal material that formed clumpsc.1 cm thick. Under these conditions, we estimated negligible (&lt;1%) effects on PM, a 12% reduction in apparent values of α, and 14% and 17% increases in values of the α‐dependent termsICRandIK,respectively.7. Our results are consistent with the hypothesis that a population‐level negative feedback (self‐shading) is responsible for sloughing in dense macroalgal beds. Sloughing was probably inevitable once macroalgal bed density and thickness surpassed a critical threshold. Cells towards the base of the bed received insufficient light to maintain metabolic balance, began to decay and weaken, and became increasingly susceptible to physical detachment from shear stress.

Diversity of nifH Genotypes in Floating Periphyton Mats Along a Nutrient Gradient in the Florida Everglades

Periphyton mats are an important component of many wetland ecosystems, performing a range of vital ecosystem functions, including nitrogen fixation. The composition and integrity of these mats are affected by nutrient additions, which might result in changes in their function. The overall objective of this study was to investigate the distribution of nifH sequences in floating periphyton mats collected along a nutrient gradient in the Florida Everglades. Distribution of nifH clone libraries indicated nutrient enrichment selected primarily for sequences branching deeply within the heterocystous cyanobacteria and within a novel group of cyanobacteria; sequences from low-nutrient sites were broadly distributed, with no clear dominance of sequences associated with heterocystous and nonheterocystous cyanobacteria and alpha-, gamma-, and delta-proteobacteria. The dominance of heterocystous cyanobacteria in nutrient-enriched sites and the lack of clear dominance by heterocystous cyanobacteria is consistent with previously reported diurnal cycles of nitrogen fixation rates in these systems. Sequences clustering with those harbored by methanotrophs were also identified; sequences from nutrient-impacted and transition regions clustered with those characteristic of type II methanotrophs, and sequences from oligotrophic regions clustered with type I methanotrophs.

Enzyme activity responses to nutrient loading in subtropical wetlands

Eutrophication caused by anthropogenic nutrient inputs is one of the greatest threats to the integrity of freshwater wetlands. The resultant changes in organic carbon cycling and nutrient mineralization may be expressed through increased decomposition rates, which are ultimately dependent on the metabolism of the resident microbial community. Specifically, microbial nutrient acquisition is controlled through the activity of enzymes, which are in turn influenced by local biogeochemical conditions. This study examines enzyme activities along distinct North-South P gradients within four distinct hydrologic units of the Florida Everglades. The results indicate that nutrient enriched sites exhibit lower N and P limitations on microbially constrained C mineralization, in addition to enhanced cellulose decomposition rates. Nutrient loading resulted in decreased microbial mobilization of resources for P mineralization, resulting in greater energetic allocation for C mineralization. Additionally, N appears to become less limiting to C mineralization in the enriched sites within Everglades National Park, the least P enriched area within the Everglades. A simple two component model, incorporating total P and the relationship between the enzymes involved in C and P mineralization accounted for between 46 and 92% of the variability in measured cellulose decomposition rates and thus demonstrates the significant influence that P loading plays in these systems. These results also suggest there is an environmental threshold TP concentration below which changes in enzyme-based resource allocation will not occur.

Soil microbial eco-physiological response to nutrient enrichment in a sub-tropical wetland

Eutrophication in subtropical wetland ecosystems can lead to extensive displacements of vegetative communities and as a result changes in overall environmental conditions (loss of indigenous habitat, substrate quality, etc.). This has generated a demand for a set of sensitive indicator(s) that prelude these structural changes. The functional response of bacterial communities may indicate the effect and extent of the impact on the overall system. The effects of nutrient enrichment on the microbial community and its ecophysiology were measured in a subtropical marsh (Water Conservation Area 2a) in the northern Everglades, USA. We investigated the microbially mediated organic matter decomposition processes and nutrient cycling in three areas of the marsh, a nutrient enriched site, an intermediate site and a unimpacted (oligotrophic) site. We chose measures associated to the hydrolytic enzyme activities of alkaline phosphatase, β-glucosidase and aminopeptidase. We also monitored microbial biomass carbon (C), nitrogen (N) and phosphorus (P) and the associated elemental turnover rates (C, N and P). We found a significant (α = 0.05) spike in microbial biomass C, N, and P in the intermediate site. The elemental turnover rates (C, N and P) where significantly higher in the impacted and intermediate site when compared to the unimpacted site. The enzymatic profiles at the unimpacted site illustrate a system regulated for optimal use of P. In the intermediate zone between the overall P-limited and P-impacted areas, the nutrient inputs alleviates the stress imposed by the P-limitation. Microbial biomass increased dramatically without a decrease in the overall microbial metabolic efficiency. The metabolic coefficients (particularly q-Potentially Mineralizable P – qPMP and qCO2) indicated that after the disturbance, the impacted areas in the Everglades are characterized by relatively open, inefficient nutrient cycles. The nonlinear shifts (threshold behavior) in microbial parameters indicate that microbial indicators function effectively as early warning signals.

Response of Biogeochemical Indicators to a Drawdown and Subsequent Reflood

Temporal oscillations in hydrology are a common occurrence in wetlands and can result in alternating flooded and drained conditions in the surface soil. These oscillations in water levels can stimulate microbial activities and result in the mobilization and redistribution of significant amounts of carbon (C), nitrogen (N), and phosphorus (P). The goal of this study was to experimentally simulate a drawdown and reflood of marsh soil from a nutrient-enriched site and a reference site of a wetland (Blue Cypress Marsh Conservation Area, Florida). The goal was to better understand the changes in biogeochemistry and microbial activities present in these soils as a result of hydrological fluctuations. Measurements of dissolved reactive phosphorus (DRP), ammonia, and nitrate in the floodwater indicated significantly higher (alpha = 0.05) NH(4)(+) and DRP fluxes from the nutrient-enriched site; floodwaters in the cores from both sites contained significant NO(3)(-) concentrations (9.6 mg N L(-1)), which was rapidly consumed over the core incubation period (30 d). Water level drawdown and reflooding initially stimulated the soil microbial biomass, methanogenic rates, and extracellular enzyme activities (acid phosphatase and beta-glucosidase). The anaerobic microbial metabolic activities (CO(2)) where initially significantly (alpha = 0.05) enhanced by the reflood, resulting in roughly equivalent rates as the aerobic respiratory activities (CO(2)), presumably as a function of the high water column NO(3)(-) levels. This study illustrates that the reflood event in the hydrological cycles in a wetland can significantly stimulate the activities of hydrolytic enzymes and microbiological communities in these soils.

Nutrient enrichment caused by in situ fish farms at Eilat, Red Sea is detrimental to coral reproduction

Recent studies report conflicting results concerning the effects of eutrophication on coral reproduction. The present study examines reproductive effort in the brooding coral Stylophora pistillata exposed to chronic eutrophication caused by in situ fish cages (FC) in the northern Gulf of Eilat (Aqaba). Histological studies of 20 S. pistillata colonies transplanted to each of two study sites, one close to the nutrient enriched FC site and the other at a reference site (IUI), 8 km southwest of the FC site, show that, overall, corals from the FC site have a significantly higher percentage of polyps containing oocytes and testes than corals from the IUI site. However, average oocyte size and the percentage of oocytes reaching the size at which fertilization occurs (i.e., >200 μm) were both significantly greater in colonies at the IUI site compared to the FC site. As the reproductive season progressed, colonies at the IUI site exhibited a decrease in the percentage of polyps containing oocytes, concomitant with an increase in the number of polyps containing planulae, indicating successful development of oocytes into planulae. In contrast, in colonies at the FC site oocyte numbers were greatest at the end of the reproductive season, and overall, numbers of planulae were significantly lower compared with the IUI colonies, suggesting relative failure of oocyte maturation, fertilization and ensuing larval development. The significantly higher lipid content found during the reproduction season in IUI colonies compared with FC colonies corroborates this assertion. This data strongly suggest that nutrients released from the fish farms have adverse effects on successful production of larvae of S. pistillata. In view of the recent severe deterioration of the coral reefs of Eilat and their present critical state of health, the only chance for their renewal is the use of immediate, prudent and rational protection measures against all man-made perturbations.

Macroalgal growth in nutrient-enriched estuaries: A biogeochemical and evolutionary perspective

Increased nutrient loading of a body of water leads to an increase in macroalgal growth. It is generally observed, however, that certain species thrive more than others, capitalising on the increased nutrient availability. These are usually small, fast-growing, ephemeral algae that often appear as nuisance blooms. This article discusses the correlation between nutrient increase and macroalgal bloom formation. From a historical perspective, the evolutionary history of nuisance macroalgae, and the habits available to them prior to anthropogenic influences on estuarine geochemistry are considered. The occurrence of macroalgal genera whose distribution is commonly related to estuaries with high nutrient loading is discussed, along with evidence suggesting that the ecophysiological traits of r-selected, ephemeral algae largely contribute to their ecological success and bloom-formation at nutrient-enriched sites.

Occurrence and reservoirs of antibiotic resistance genes in the environment

Antibiotic resistance genes have become highly mobile since the development of antibiotic chemotherapy. A considerable body of evidence exists proving the link between antibiotic use and the significant increase in drug-resistant human bacterial pathogens. The application of molecular detection and tracking techniques in microbial ecological studies has allowed the reservoirs of antibiotic resistance genes to be investigated. It is clear that the transfer of resistance genes has occurred on a global scale and in all natural environments. The considerable diversity of bacteria and mobile elements in soils has meant that the spread of resistance genes has occurred by all currently known mechanisms for bacterial gene transfer. Trans-kingdom transfers from plants to bacteria may occur in soil. Hot spots for gene transfer in the soil/plant environment have been described and colonized niches such as the rhizosphere and other nutrient-enriched sites, for example manured soil, have been identified as reservoirs of resistance genes. Although exposure and selection for tolerance of antibiotics is considerable in clinical environments there is increasing evidence that selection for resistant phenotypes is occurring in natural environments. Antibiotic-producing bacteria are abundant in soil and there is evidence that they are actively producing antibiotics in nutrient-enriched environments in soil. In addition there is clear evidence that the self-resistance genes found within antibiotic gene clusters of the producers have transferred to other non-producing bacteria. Perhaps most important of all is the use of antibiotics in agriculture as growth promotants and for treatment of disease in intensively reared farm animals. These treatments have resulted in gut commensal and pathogenic bacteria acquiring resistance genes under selection and then, due to the way in which farm slurries are disposed of, the spread of these genes to the soil bacterial community. Integrons with multiple resistance gene cassettes have been selected and disseminated in this way; many of these cassettes carry other genes such as those conferring heavy metal and disinfectant resistance which have been co-selected in bacteria surviving in effluents and contaminated soils, further maintaining and spreading the antibiotic resistance genes.