Removal of pesticide mixtures in a stormwater wetland collecting runoff from a vineyard catchment

Wetlands can collect contaminated runoff from agricultural catchments and retain dissolved and particle-laden pesticides. However, knowledge about the capacity and functioning of wetland systems with respect to the removal of pesticides is very limited. Here we show that stormwater wetlands can efficiently remove pesticides in runoff from vineyard catchments during the period of pesticide application, although flow and hydrochemical conditions of the wetland largely vary over time. During the entire agricultural season, the inflowing load of nine fungicides, six herbicides, one insecticide and four degradation products was 8.039 g whereas the outflowing load was 2.181 g. Removal rates of dissolved loads by the wetland ranged from 39% (simazine) to 100% (cymoxanil, gluphosinate, kresoxim methyl and terbuthylazine). Dimethomorph, diuron, glyphosate, metalaxyl and tetraconazole were more efficiently removed in spring than in summer. More than 88% of the input mass of suspended solids was retained, underscoring the capability of the wetland to trap pesticide-laden particles via sedimentation. Only the insecticide flufenoxuron was frequently detected in the wetland sediments. Our results demonstrate that stormwater wetlands can efficiently remove pesticide mixtures in agricultural runoff during critical periods of pesticide application, although fluctuations in the runoff regime and hydrochemical characteristics can affect the removal rates of individual pesticides.     

Effect of watershed parameters on mercury distribution in different environmental compartments in the Mobile Alabama River Basin, USA

Total mercury (THg) and mono-methylmercury (MeHg) levels in water, sediment, and largemouth bass (LMB) (Micropterus salmoides) were investigated at 52 sites draining contrasting land use/land cover and habitat types within the Mobile Alabama River Basin (MARB). Aqueous THg was positively associated with iron-rich suspended particles and highest in catchments impacted by agriculture. Sediment THg was positively associated with sediment organic mater and iron content, with the highest levels observed in smaller catchments influenced by wetlands, followed by those impacted by agriculture or mixed forest, agriculture, and wetlands. The lowest sediment THg levels were observed in main river channels, except for reaches impacted by coal mining. Sediment MeHg levels were a positive function of sediment THg and organic matter and aqueous nutrient levels. The highest levels occurred in agricultural catchments and those impacted by elevated sulfate levels associated with coal mining. Aqueous MeHg concentrations in main river channels were as high as those in smaller catchments impacted by agriculture or wetlands, suggesting these areas were sources to rivers. Elevated Hg levels in some LMB were observed across all types of land use and land cover, but factors such as shallow water depth, larger wetland catchment surface area, low aqueous potassium levels, and higher Chl a concentrations were associated with higher Hg burdens, particularly in the Coastal Plain province. It is suggested that the observed large variability in LMB Hg burdens is linked to fish displacement by anglers, differences in food web structure, and sediment biogeochemistry, with surficial sediment iron oxides buffering the flux of MeHg from sediments to deeper water pelagic food webs.     

Wetland types and wetland maps differ in ability to predict dissolved organic carbon concentrations in streams

Three categories of digital wetland maps widely available in the United States were used to develop models relating wetlands to DOC: (1) wetlands mapped by the U.S. National Wetlands Inventory (NWI) (2) wetland vegetation cover mapped by the U.S. National Land Cover Dataset (NLCD), and (3) maps of hydric soils. Data extracted from these maps for 27 headwater catchments of the Ontonagon River in northern Michigan, USA were used with DOC concentrations measured in catchment streams to develop stepwise multiple regressions based on wetland area and type. The catchments of the 27 tributaries ranged in area from 2 to 66 km(2) and wetlands constituted 10 to 53% of their area. Although all three databases provided regressions that were highly significant (p<0.001), the variance explained was greater for NWI maps (R(2)=0.75) than for NLCD (R(2)=0.61) or soil maps (R(2)=0.60). Wetland-stream relationships were strongest during September 2002, but were significant for nine out of ten dates sampled during subsequent seasons. The individual wetland type most highly correlated (r>0.62) with stream DOC concentrations was conifer peatland, represented on the NWI maps as Palustrine Needle-leaved Forest, the NLCD maps as woody wetland, and the soil maps as organic soils. For the NWI dataset, DOC was negatively correlated with area of palustrine emergent wetlands (i.e., sedge meadows and graminoid fens) and bog shrubs, inferring that these wetland types may be sinks for DOC. Because of the different effects of wetland vegetation types on DOC, a GIS data source such as the NWI which depicts those wetland types is superior for predicting landscape contributions to stream DOC concentrations.     

Loss rates of urban biocides can exceed those of agricultural pesticides

Biocides and pesticides are used to control unwanted organisms in urban and agricultural areas. After application, they can be lost to surface waters and impair water quality. Several national consumption studies have shown that urban and agricultural use may be in the same range. It is difficult to judge whether this results in similar loadings of surface waters because there is a lack of sound, comparative studies addressing urban and agricultural losses simultaneously.The aim of this study is thus to relate the biocide and pesticide loads found in surface waters to their respective urban and agricultural usage (loss rates). To simultaneously assess the loss rates, we conducted a comprehensive field study in a catchment of mixed land use on the Swiss Plateau. The study area was divided into four sub-catchments with different degrees of urban and agricultural land use. In addition, we studied the only wastewater treatment plant, a combined sewer overflow and a storm sewer within the area. Rain events were sampled at high temporal resolution from March to November, 2007. Information on agricultural applications was gained from local farmers. For urban uses, consumption estimations were conducted based on statistical and product information.Despite substantially lower amounts used, the measured loads of urban biocides were in the same range as the most widely-used agricultural pesticides. The lower usage was compensated by urban loss rates that were up to ten times higher than agricultural ones (0.6 to 15% for urban, 0.4 to 0.9% for agricultural compounds). For most biocides and pesticides, the loads were controlled by rain events. Besides the rain-controlled losses, some urban-used biocides (e.g. diazinon) showed a continuous load independent of rain events and season. This study demonstrates that in catchments with mixed land use, mitigation strategies have to pay sufficient attention to the urban sources.     

Effect of constructed wetlands receiving agricultural return flows on disinfection byproduct precursors

The effects of wetland treatment on disinfection byproduct precursors were evaluated for six constructed wetlands receiving agricultural return flows in the Central Valley of California. Wetlands varied in size, age, vegetation, hydrologic residence time (0.9-20 days) and water management (continuous flow vs. flood pulse). The effects of wetland treatment were determined by analyzing input and outflow waters for dissolved organic carbon concentration and quality, bromide concentration, and formation potentials for nine disinfection byproduct species, including trihalomethanes, haloacetronitriles, chloral hydrate, and haloketones. We hypothesized that hydraulic residence time was a key factor governing differences in disinfection byproduct precursors. Small wetlands (<3 ha) with short hydraulic residence times (<2 days) did not produce significant changes in disinfection byproduct precursor concentrations with respect to the agricultural return flows input to the wetlands. In these wetlands hydraulic residence times were not long enough to promote processes that adversely affect dissolved organic carbon and bromide quantity, such as evapoconcentration and leaching from vegetation. Thus, less negative effects were associated with disinfection byproduct formation. In contrast, larger wetlands (>100 ha) with long hydraulic residence times (>10 days) resulted in higher dissolved organic carbon and bromide levels, increasing disinfection byproduct formation by factors ranging between 1.7 and 10.2 compared to agricultural return flows. Results from this study provide important information for optimizing the design and management of constructed wetlands to effectively combine control of disinfection byproduct precursors with other water quality parameters.     

Mercury dynamics of a temperate forested wetland

Wetlands have been identified as important sites of mercury methylation in catchments, but the range of wetland types and their geographic distribution for which methylmercury fluxes are reported in the literature are limited. Linkages among wetland hydrology, total mercury and methylmercury concentrations and fluxes, and other water quality parameters were assessed in a temperate forested swamp in Southern Ontario, Canada. Two hydrogeomorphically distinct stream reaches within the wetland exhibited differences in wetland-stream hydrologic connectivity, which strongly influenced mercury dynamics. Total mercury flux from both reaches to the downstream was highest during flow conditions in which the wetland and stream were hydrologically connected. The wetland as a whole was a net sink for total mercury and a net source for methylmercury to the downstream system. Both total mercury and methylmercury concentrations were related to dissolved and particulate organic carbon in stream waters, but these relationships were dependent upon the sampling location and flow conditions. Throughout the wetland, methylmercury concentrations exhibited temporal relationships with sulfate concentrations. Further, despite short surface water residence times, periods of wetland and stream disconnect and high pH (approx. 8) in surface water, methylmercury fluxes from this wetland to the downstream were similar to those from more stagnant and acidic wetlands.     

A multi‐component method to determine pesticides in surface water by liquid‐chromatography tandem quadrupole mass spectrometry

Pesticide pollution of surface water is a major concern in many agricultural catchments The development of rapid and accurate methods for determining pesticide concentrations in water samples is, therefore, important. Here we describe a method for the simultaneous analysis of six pesticides (metaldehyde, quinmerac, carbetamide, metazachlor, propyzamide and pendimethalin) in natural waters by direct aqueous injection with liquid chromatography‐tandem mass spectrometry. The method validation showed good linearity from 0.2 to 50.0 µg/L with correlation coefficients between 0.995 and 0.999. Method accuracy ranged from 84 to 100% and precision Relative standard deviation (RSD) from 4 to 15%. The limits of detection for the targeted pesticides ranged from 0.03 to 0.36 µg/L. No significant matrix effects on quantification were observed (t‐test). The method was tested on water samples from a small arable catchment in eastern England. Peak concentrations for the determinands ranged from 1 to 10 µg/L.     

Significance of urban and agricultural land use for biocide and pesticide dynamics in surface waters

Biocides and pesticides are designed to control the occurrence of unwanted organisms. From their point of application, these substances can be mobilized and transported to surface waters posing a threat to the aquatic environment. Historically, agricultural pesticides have received substantially more attention than biocidal compounds from urban use, despite being used in similar quantities.This study aims at improving our understanding of the influence of mixed urban and agricultural land use on the overall concentration dynamics of biocides and pesticides during rain events throughout the year. A comprehensive field study was conducted in a catchment within the Swiss plateau (25 km²). Four surface water sampling sites represented varying combinations of urban and agricultural sources. Additionally, the urban drainage system was studied by sampling the only wastewater treatment plant (WWTP) in the catchment, a combined sewer overflow (CSO), and a storm sewer (SS). High temporal resolution sampling was carried out during rain events from March to November 2007.The results, based on more than 600 samples analyzed for 23 substances, revealed distinct and complex concentration patterns for different compounds and sources. Five types of concentration patterns can be distinguished: a) compounds that showed elevated background concentrations throughout the year (e.g. diazinon >50 ng L⁻¹), indicating a constant household source; b) compounds that showed elevated concentrations driven by rain events throughout the year (e.g. diuron 100-300 ng L⁻¹), indicating a constant urban outdoor source such as facades; c) compounds with seasonal peak concentrations driven by rain events from urban and agricultural areas (e.g. mecoprop 1600 ng L⁻¹ and atrazine 2500 ng L⁻¹ respectively); d) compounds that showed unpredictably sharp peaks (e.g. atrazine 10,000 ng L⁻¹, diazinon 2500 ng L⁻¹), which were most probably due to improper handling or even disposal of products; and finally, e) compounds that were used in high amounts but were not detected in surface waters (e.g. isothiazolinones).It can be safely concluded that in catchments of mixed land use, the contributions of biocide and pesticide inputs into surface waters from urban areas are at least as important as those from agricultural areas.     

Export of dissolved organic matter in relation to land use along a European climatic gradient

The terrestrial export of dissolved organic matter (DOM) is associated with climate, vegetation and land use, and thus is under the influence of climatic variability and human interference with terrestrial ecosystems, their soils and hydrological cycles. We present a data-set including catchments from four areas covering the major climate and land use gradients within Europe: a forested boreal zone (Finland), a temperate agricultural area (Denmark), a wet and temperate mountain region in Wales, and a warm Mediterranean catchment draining into the Gulf of Lyon. In all study areas, DOC (dissolved organic carbon) was a major fraction of DOM, with much lower proportions of DON (dissolved organic nitrogen) and DOP (dissolved organic phosphorus). A south-north gradient with highest DOC concentrations and export in the northernmost catchments was recorded: DOC concentrations and loads were highest in Finland and lowest in France. These relationships indicate that DOC concentrations/export are controlled by several factors including wetland and forest cover, precipitation and hydrological processes. DON concentrations and loads were highest in the Danish catchments and lowest in the French catchments. In Wales and Finland, DON concentrations increased with the increasing proportion of agricultural land in the catchment, whereas in Denmark and France no such relationship was found. DOP concentrations and loads were low compared to DOC and DON. The highest DOP concentrations and loads were recorded in catchments with a high extent of agricultural land, large urban areas or a high population density, reflecting the influence of human impact on DOP loads.     

Modelling Cryptosporidium oocysts transport in small ungauged agricultural catchments

Cryptosporidium is an environmentally robust pathogen that has caused severe waterborne disease outbreaks worldwide. The main source of zoonotic Cryptosporidium parvum oocysts in human drinking water is likely to be from farm animals via catchment pathways with water as the main transport vector. The vast majority of small agricultural catchments are ungauged therefore it is difficult to use a process model to predict and understand the mechanisms and activities that regulate the risk of surface water contamination from agricultural areas. For this study, two ungauged agricultural catchments in Ireland were used to model Cryptosporidium oocyst transport using SWAT2005 on a daily basis with reference data from adjacent catchment gauging stations. The results indicated that SWAT2005 could simulate stream flow with good agreement between prediction and observation on a monthly basis (R² from 0.94 to 0.83 and E (efficiency) from 0.92 to 0.66), but Cryptosporidium oocyst concentration results were less reliable (R² from 0.20 to 0.37, P < 0.05; with poor E −0.37 to −2.57). A sensitivity analysis using independent parameter perturbation indicated that temperature was the most important parameter regulating oocyst transport in the study catchments and that the timing of manure application relative to the occurrence of water runoff event was critical. The results also showed that grazing management had little influence on predicted oocyst transport while fields fertilized with manure were the key critical source areas for microbial contaminations in the study catchments. It was concluded that the approach presented could be used to assist with understanding the epidemiology of waterborne cryptosporidiosis outbreaks and to improve catchment management for the safety of the general public health.     

Atrazine mineralization potential in two wetlands

The fate of atrazine in agricultural soils has been studied extensively but attenuation in wetland systems has received relatively little attention. The purpose of this study was to evaluate the mineralization of atrazine in two wetlands in central Ohio. One was a constructed wetland, which is fed by Olentangy River water from an agricultural catchment area. The other was a natural fen (Cedar Bog) in proximity to atrazine-treated cornfields. Atrazine mineralization potential was measured by 14CO2 evolution from [U-ring-14C]-atrazine in biometers. The constructed wetland showed 70-80% mineralization of atrazine within 1 month. Samples of wetland water that were pre-concentrated 200-fold by centrifugation also mineralized 60-80% of the added atrazine. A high extent of atrazine mineralization (75-81% mineralized) was also associated with concentrated water samples from the Olentangy River that were collected upstream and downstream of the wetland. The highest levels of mineralization were localized to the top 5 cm zone of the wetland sediment, and the activity close to the outflow at the Olentangy wetland was approximately equal to that near the inflow. PCR amplification of DNA extracted from the wetland sediment samples showed no positive signals for the atzA gene (atrazine chlorohydrolase), while Southern blots of the amplified DNA showed positive bands in five of the six Olentangy wetland sediment samples. Amplification with the trzD (cyanuric acid amidohydrolase) primers showed a positive PCR signal for all Olentangy wetland sediment samples. There was little mineralization of atrazine in any of the Cedar Bog samples. DNA extracted from Cedar Bog samples did not yield PCR products, and the corresponding Southern hybridization signals were absent. The data show that sediment microbial communities in the Olentangy wetland mineralize atrazine. The level of activity may be related to the seasonality of atrazine runoff entering the wetland. Comparable activity was not observed in the Cedar Bog, perhaps because it does not directly receive agricultural runoff. Qualitatively, the detection of the genes was associated with measurable mineralization activity which was consistent with the differences between the two study sites.     

Spatial heterogeneity of the spring flood acid pulse in a boreal stream network

Spatial and temporal patterns in streamwater acidity are ecologically important, but difficult to measure in parallel. Here we present the spatial distribution of streamwater chemistry relevant to acidity from 60 stream sites distributed throughout a 67 km² boreal catchment, sampled during a period of winter baseflow (high pH) and during a spring flood episode (low pH). Sites were grouped based on pH level and pH change from winter baseflow to spring flood. The site attributes of each pH group were then assessed in terms of both stream chemistry and subcatchment landscape characteristics. Winter baseflow pH was high throughout most of the stream network (median pH 6.4), but during the spring flood episode stream sites experienced declines in pH ranging from 0-1.6 pH units, resulting in pH ranging from 4.3-6.3. Spring flood pH was highest in larger, lower altitude catchments underlain by fine sorted sediments, and lowest in small, higher altitude catchments with a mixture of peat wetlands and forested till. Wetland-dominated headwater catchments had low but stable pH, while the spring flood pH drop was largest in a group of catchments of intermediate size which contained well-developed coniferous forest and a moderate proportion of peat wetlands. There was a trend with distance downstream of higher pH, acid neutralizing capacity (ANC) and base cation concentrations together with lower dissolved organic carbon (DOC, strongly negatively correlated with pH). This apparent scale-dependence of stream chemistry could be explained by a number of environmental factors which vary predictably with altitude, catchment area and distance downstream—most notably, a shift in surficial sediment type from unsorted till and peat wetlands to fine sorted sediments at lower altitudes in this catchment. As a result of the combination of spatial heterogeneity in landscape characteristics and scale-related processes, boreal catchments like this one can be expected to experience high spatial variability both in terms of chemistry at any given point in time, and in the change experienced during high discharge episodes. Although chemistry patterns showed associations with landscape characteristics, considerable additional variability remained, suggesting that the modeling of dynamic stream chemistry from map parameters will continue to present a challenge.     

Statutory Water Quality Objectives on the River Cam

The Government has announced its wishes to gradually introduce statutory water quality objectives in pilot catchments, commencing in late 1993. The River Cam is one of the catchments under consideration.
The paper describes the main physical features of the River Cam and its uses, which include salmonid and cyprinid fisheries, agricultural and industrial abstraction, and recreational pursuits.
Significant sewage and industrial discharges in the catchment, and their impact on water quality, are discussed, and current river quality is compared with established river quality objectives, EC requirements and proposed statutory water quality objectives. Procedures for setting the latter objectives are considered, together with monitoring and compliance assessment. Future effluent discharge standards are proposed, and options to achieve long-term water quality targets are suggested as part of a catchment management action plan.     

Assessing sediment and water quality issues in expanding African wetlands: the case of the Mara River,Tanzania

Climatological influences and catchment pressures have altered the natural energy regime in the lower Mara River in Tanzania, creating conditions favourable for sedimentation. Wetland growth in the lower Mara River is investigated through particle size analyses and high resolution micro-XRF screening of sediment cores from the area. Geochemical profiling indicates that the Mara wetlands serve as an important trap for contaminated sediments originating the North Mara Gold Mine complex. Heavy metals and arsenic (As) appear to be reasonably well bound in alluvial stores of the wetlands but selected elements (e.g. Cr) may become progressively mobile over time. Human activity in the catchment presents risks to the biodiversity of the wetland area, and also to its ability to buffer Lake Victoria by assimilating pollutants. Changes to the hydrological regime of the Mara wetlands could reverse the patterns of sedimentation and adversely affect water and sediment quality in Lake Victoria. Furthermore, the study highlights a deficit of data relating to sediment sources, deposition patterns and associated contamination, which must be understood before effective management strategies on sediment and contaminants can be applied.     

Decline of wetland ecosystems in the coastal plain of Israel during the 20th century: Implications for wetland conservation and management

Severe competition for water and augmented agricultural and urban development in Israel have modified and destroyed wetland habitats. Using historical maps, we mapped the past extent of swamps and natural rain pools along the central coastal plain of Israel and compared this with the present extent as reflected in reports, field surveys and satellite images. Out of 192 swamps and rain pools recorded in historical sources, only 18% (35) still exist today. Extrapolation from 69 new records of rain pools (missing in historical sources), suggests that in the 19th century, before many of the wetlands were drained, transformed to agricultural land, or built over, the number of wetland habitats in the coastal plain was threefold higher. In addition to reduction of wetland number, human activity has also diminished wetland size. In rainy winters wetland areas in the coastal plain in the past were an order of magnitude larger than they are today (27.6 and 2.4 km², respectively). At present, the existing natural water bodies along the coastal plain are temporary, small, and surrounded by built-up areas and roads. The grave state of the wetlands in Israel underscores the urgent need for protection of the remnant wetland sites. Following the successful example of wetland restoration in the Hula Valley, we recommend restoring various historical wetlands that have been drained.     

Agricultural pesticides threaten the ecological integrity of northern prairie wetlands.

The northern Great Plains of North America has millions of small wetlands, and these are often dispersed through cultivated fields. We investigated relationship between pesticide occurrence and precipitation in selected wetlands in a 30.4 x 10(4) km2 area of the Great Plains with relatively uniform farming practices and 1,777,600 wetlands (southern Saskatchewan, Canada). By early July after pesticides have been applied to crops, the mean number of pesticides detected in wetlands ranged from 1.8 in regions with little precipitation (< 21 mm rain during the previous 15 days) to 3.2 in regions under higher rainfall (> 90 mm). The proportion of wetlands in which at least one pesticide exceeded Canadian guidelines for the protection of aquatic life increased from 0% to 60% over this same precipitation range. The maximum number of pesticides detected in a single wetland was six. Concentration of lindane in wetlands increased with increasing precipitation. Using geographic information on rainfall, wetland densities, area seeded to crops, and region specific relationships between pesticides and precipitation, we estimated the number of wetlands in Saskatchewan with elevated levels of pesticides. In early July, during 3 of the 6 years, the number of wetlands subjected to pesticide levels that exceeded guidelines for the protection of aquatic life was significant, ranging from 152,000 to 424,000 wetlands or 9-24%, respectively, of the total. Lindane and triallate exceeded the guidelines most frequently.     

Catchment-specific element signatures in estuarine crocodiles (Crocodylus porosus) from the Alligator Rivers Region, northern Australia

The concentrations of Na, K, Ca, Mg, Ba, Sr, Fe, Al, Mn, Zn, Pb, Cu, Ni, Cr, Co, Se, U and Ti were determined in the osteoderms and/or flesh of estuarine crocodiles (Crocodylus porosus) captured in three adjacent catchments within the Alligator Rivers Region (ARR) of northern Australia. Results from multivariate analysis of variance showed that when all metals were considered simultaneously, catchment effects were significant (P < or = 0.05). Despite considerable within-catchment variability, linear discriminant analysis (LDA) showed that differences in elemental signatures in the osteoderms and/or flesh of C. porosus amongst the catchments were sufficient to classify individuals accurately to their catchment of occurrence. Using cross-validation, the accuracy of classifying a crocodile to its catchment of occurrence was 76% for osteoderms and 60% for flesh. These data suggest that osteoderms provide better predictive accuracy than flesh for discriminating crocodiles amongst catchments. There was no advantage in combining the osteoderm and flesh results to increase the accuracy of classification (i.e. 67%). Based on the discriminant function coefficients for the osteoderm data, Ca, Co, Mg and U were the most important elements for discriminating amongst the three catchments. For flesh data, Ca, K, Mg, Na, Ni and Pb were the most important metals for discriminating amongst the catchments. Reasons for differences in the elemental signatures of crocodiles between catchments are generally not interpretable, due to limited data on surface water and sediment chemistry of     

Defining the sources of low-flow phosphorus transfers in complex catchments

Nutrient transfers from the land to rivers have the potential to cause persistent eutrophic impacts at low flows even though the transfers may constitute a minor percentage of total annual fluxes. In rural catchments, the contribution from agricultural soils during storm events can be particularly large and untangling the relative contributions from multiple sources that vary in time and space is especially problematic. In this study, the potential for domestic septic tank system pollution during low flows was investigated in 3 small catchments (3 to 5 km(2)) using an integrated series of methods. These included septic system surveys, continuous (10 min) total phosphorus (TP) monitoring at the outlet of each catchment, repeated low-flow water quality surveys in sub-catchments upstream of the catchment outlets and single day river-walk water quality surveys. A series of faecal matter and grey-water fingerprinting techniques were also employed. These included determining sterol ratios in stream sediments, monitoring the presence of proteins, E. coli and enterococci bacterial signatures and boron. The total density and density of poorly maintained septic systems mirrored the magnitude of frequent TP concentrations in the catchments although this relationship was less apparent in the nested sub-catchments. The exception was possibly related to the simple hydraulics in one particular catchment and indicated temporary effluent attenuation in the other catchments. Repeated low-flow and river-walk water quality surveys highlighted discrete areas and reaches where stepped changes in nutrient concentration occurred. Bio-chemical fingerprinting showed that between 7% and 27% of sediments were contaminated with human faecal material and correlation matrices indicated that, at least during low flows, P fractions were positively correlated with some markers of faecal and grey-water contamination.     

Distribution of inland wetlands with sulfidic sediments in the Murray-Darling Basin, Australia

This project examined the extent of sulfidic sediments in freshwater wetlands of the Murray-Darling Basin, Australia. We sampled 81 wetlands throughout the basin with methods previously developed for the analysis of coastal acid sulfate soils. Sulfidic sediments are generally regarded as a coastal phenomenon. We tested the hypothesis that elevated concentrations of mineral sulfides may also accumulate in sediments of inland wetlands. Of the 81 wetlands sampled, 17 (21%) contained reduced sulfur in sediments at concentrations above suggested trigger values. Most of the affected wetlands were adjacent to the Murray River, with only several associated with other major river catchments. Reduced sulfur in the sediments was positively correlated with sulfate concentrations in the overlying water column. This represents a concern for wetland managers because of the increasing desire to return wetlands to a more natural wetting and drying cycle to improve wetland health. However, during drying, sulfidic sediments oxidise and produce acid, which may exceed the buffering capacity of the system and ultimately harm aquatic life. Therefore, if sulfidic sediments are present, a drying phase should only be reinstated after careful consideration of the potential acidification risks. This study verified that sulfidic sediments can occur in freshwater wetlands in concentrations that could pose an ecological risk if mismanaged.