Stream Water Concentrations Research Articles

Sources of dissolved organic carbon in small volcanic mountainous tropical rivers, examples from Guadeloupe (French West Indies)

In the tropical zone, small watersheds are affected by intense meteorological events. These events play an important role in the erosion of soils and therefore on the sources of organic carbon in small tropical rivers. We studied the geochemistry of two soils on Basse-Terre Island (French West Indies, FWI): ferralitic soil and Andosol. The two studied soils are very similar in terms of soil organic matter (SOM) and soil solution parameters. The total organic carbon (TOC) and total nitrogen (TN) contents vary between 1.7 and 92g kg‐1 and between 0.1 and 5.5g kg‐1, respectively, with the highest concentrations observed in the topsoil. The C/N ratios are relatively constant throughout the soil profiles (ca. 12). The carbon isotopic composition of SOM varies between ‐27.3‰ and ‐22.7‰ and presents an enrichment with increasing depth of soil profiles. Dissolved organic carbon (DOC) concentrations in soil solutions, varying from 3.2 to 91.3mg L‐1, are similar for the both extraction used in lab (with milliQ water and Ca(NO3)2) but are higher than those measured in soil solutions sampled from lysimeters (0.65–1.46mg L‐1). The isotopic compositions of DOC obtained by extractions and SOM are comparable, with δ13C values ranging from ‐28.6‰ to ‐25.8‰. The DOC sampled from lysimeters is systematically depleted in 13C compared to DOC obtained by extractions, with δ13C values of ‐33.8‰ to ‐30.6‰. The enrichment of δ13C of SOM through the soil profiles is either consistent with the carbon isotopic fractionation of SOM by decomposing organisms, or the differential mineralization of both labile and stable carbon stocks in soils. DOC concentrations in stream waters vary between 0.46 and 5.75mg L‐1, and are generally lower during low water level than floods. The isotopic compositions of DOC in the rivers range from ‐38.9‰ to ‐27.2‰, with δ13C values, which are more depleted in 13C during low water level than flood events. The δ13CDOC of water river samples and soil solutions obtained by extraction and collected with lysimeters demonstrates that the DOC in rivers derives essentially from both the lixiviation of the soil surface layers during floods and groundwater flow during low water levels. Lixiviation of soil surface layers can be boosted by significant increases of intensity and duration of meteorological events and can strongly favor the release of surface soil organic matter in rivers and the impoverishment in nutrients of soil surface layers.

Anthropogenic gadolinium as a transient tracer for investigating river bank filtration

The growing use of gadolinium-based contrast agents in magnetic resonance imaging (MRI) leads to an increasing input of anthropogenic gadolinium (Gdanth) into natural environments. Conventional sewage treatment is unable to remove Gdanth and since MRI facilities are mainly used on weekdays the Gdanth inputs to sewage treatment plants are generally higher between Monday and Friday. This transient signal has been traced in both surface water and groundwater through 12-h composite samples collected at high spatial resolutions using depth-discrete rhizon samplers. Propagation of the Gdanth signal from surface water to groundwater was used to calibrate lumped parameter models. Transit time distributions derived for each sampling site revealed mean transit times of between 0.5 and 10days. Other metrics, such as peak transit time, were shown to correlate better with observed time lags between peak Gdanth concentrations in stream water and groundwater. The relatively stable artificial sweetener acesulfame was investigated as a possible additional sewage indicator, but decreasing concentrations along the flow path indicated its attenuation. We have demonstrated that the ideal tracer Gdanth occurs transiently and can be used to derive groundwater transit times.

Phosphorus source-sink relationships of stream sediments in the Rathbun Lake watershed in southern Iowa, USA.

The surface waters of Rathbun Lake watershed in southern Iowa are impacted by agricultural sources of sediments and nutrients, including phosphorus (P). Because stream sediments often play an important role in regulating P concentrations in stream water, we investigated sediment-water column P relationships in four creeks within the watershed and then evaluated the relationship between sediment properties and indicators of the risk of P loss. Based on Mehlich-3-extractable P (17 to 68mgkg(-1)) and degree of P saturation (2 to 12%), stream bank and bed sediments at the four sites were unlikely to serve as major sources of P. However, equilibrium P concentrations, which ranged from 0.02 to 0.12mgL(-1), indicated that bed sediments could release P to the water column depending on dissolved P (DP) concentrations in the stream water and the time of year. The likelihood of P desorption from the sediments increased with increasing pH (r = 0.92, p < 0.01) and sand content (r = 0.78, p < 0.05), but decreased with clay content (r = -0.72, p < 0.05) and iron (Fe) (r = -0.93, p < 0.001) associated with organic matter. From these results, we speculate that changes in land use within the riparian areas may, at least initially, have little effect on P concentrations in the streams. Low concentrations of DP relative to total P (TP) in these streams, however, suggest that P loads to Rathbun Lake can be reduced if P inputs from eroded bank sediments are controlled.

Stream Water Nitrogen Eutrophication During Non-Irrigated Periods in a Paddy-Dominated Agricultural Basin in a Snowfall Area in Japan

We measured the concentrations of dissolved inorganic nitrogen (DIN; nitrate, ammonium, and nitrite) in stream water in a paddy-dominated agricultural basin in a snowfall area from August 2009 to October 2010 to facilitate evaluation of stream water eutrophication from nitrogen during the non-irrigated period. We compared the nitrogen budget in a paddy field between irrigated and non-irrigated periods, from information about nitrogen fertilizer, denitrification, harvested rice, and atmospheric nitrogen deposition. We also estimated stream nitrogen exports from DIN concentrations and stream flow rates. DIN concentrations in stream water were higher during the non-irrigated period (October–March) than during the irrigated period (April–September). Stream flow was also higher during the non-irrigated period (5.9 mm day−1) than during the irrigated period (2.5 mm day−1), which possibly reflects snow melting. Although nitrogen fertilizer was applied during the irrigated period, the amount of nitrogen removed by the rice harvest and denitrification was sufficiently large to reduce nitrogen exports from paddy fields. Atmospheric nitrogen deposition was higher during the non-irrigated period (755 kg N km−2) than during the irrigated period (410 kg N km−2). DIN exports were also higher in the non-irrigated period (860 kg N km−2) than in the irrigated period (120 kg N km−2). The higher exports in the non-irrigated period may reflect the lack of nitrogen removal by a rice harvest and denitrification and increased runoff and higher atmospheric nitrogen deposition. Our study highlights the important contribution of the non-irrigated period to nitrogen eutrophication in stream water in this particular environment.

The characteristics of soil N transformations regulate the composition of hydrologic N export from terrestrial ecosystem

AbstractIt is important to clarify the quantity and composition of hydrologic N export from terrestrial ecosystem and its primary controlling factors, because it affected N availability, productivity, and C storage in natural ecosystems. The most previous investigations were focused on the effects of N deposition and human disturbance on the composition of hydrologic N export. However, few studies were aware of whether there were significant differences in the concentrations and composition of hydrologic N export from natural ecosystems in different climate zones and what is the primary controlling factor. In the present study, three natural forest ecosystems and one natural grassland ecosystem that were located in different climate zones and with different soil pH range were selected. The concentrations of total dissolved N, dissolved organic nitrogen (DON), NH4+, NO3− in soil solution and stream water, soil properties, and soil gross N transformation rates were measured to answer above questions. Our results showed that NO3− concentrations and the composition pattern of hydrologic N export from natural ecosystems varied greatly in the different climate zones. The NO3− concentrations in stream water varied largely, ranging from 0.1 mg N L−1 to 1.6 mg N L−1, while DON concentration in stream water, ranging from 0.1 to 0.9 mg N L−1, did not differ significantly, and the concentrations of NH4+ were uniformly low (average 0.1 mg N L−1) in all studied sites. There was a trade‐off relationship between the proportions of NO3− and DON to total dissolved N in stream water. In subtropical strongly acidic forests soil site, DON was the dominance in total dissolved N in stream water, while NO3−‐N became dominance in temperate acidic forests soil site, subtropical alkaline forests soil region, and the alpine meadow sites on the Tibetan Plateau. The proportions of NO3− to total dissolved N in both soil solution and stream water significantly increased with the increasing of the gross autotrophic nitrification rates (p &lt; 0.01). Our results indicated that the characteristics of soil N transformations were the most primary factor regulating the composition of hydrologic N losses from ecosystems. The nitrification was the central soil N transformation processes regulating N composition in soil solution and hydrologic N losses. These results provided important information on understanding easily the composition of hydrologic N export from terrestrial ecosystem.

Fecal Indicator Bacteria Entrainment from Streambed to Water Column: Transport by Unsteady Flow over a Sand Bed

Storms cause a substantial increase in the fecal indicator bacteria (FIB) concentrations in stream water as a result of FIB-laden runoff and the release of FIB from stream sediments. Previous work has emphasized the association between FIB and bed sediments finer than sand. The objectives of this work were to elucidate the effect of various velocities on the entrainment of bed-dwelling coliforms in sand-bed streams and to refine methodologies for quantifying sandy streambeds as sources of FIB. Pump-induced hydrographs were created using a stainless steel nonrecirculating flume. Experiments consisted of simulating four storm hydrographs and collecting water samples upstream and downstream of a sand bed at selected intervals. Bed sediment samples were collected before and after each event. The highest concentrations of total coliform and suspended sediments generally occurred in the downstream samples during the rising limb of the hydrographs as a result of entrainment of coliforms and sand from the bed to the water column. There was a first flush effect in the system, as the upper layer of sand was influenced by a rapidly increasing velocity at ∼0.2 m s. Coliforms downstream of the sand bed increased rapidly as velocity exceeded this threshold but then declined even as velocity and discharge continued to increase. This likely reflects the depletion of coliforms as the more densely populated sediment layer was flushed out. There is evidence that streams with sand beds harbor enough FIB that development of total maximum daily loads (TMDLs) should include consideration of them as a source.

Press or pulse exposures determine the environmental fate of cerium nanoparticles in stream mesocosms.

Risk-assessment models indicate that stream ecosystems receiving municipal wastewater effluent may have the greatest potential for exposure to manufactured nanoparticles. The authors determined the fate of cerium oxide (CeO2 ) nanoparticles in outdoor stream mesocosms using 1) 1-time pulse addition of CeO2 nanoparticles, representative of accidental release, and 2) continuous, low-level press addition of CeO2 nanoparticles, representative of exposure via wastewater effluent. The pulse addition led to rapid nanoparticle floc formation, which appeared to preferentially deposit on periphyton in low-energy areas downstream from the location of the input, likely as a result of gravitational sedimentation. Floc formation limited the concentration of suspended nanoparticles in stream water to <5% of target and subsequent downstream movement. In contrast, press addition of nanoparticles led to higher suspended nanoparticle concentrations (77% of target) in stream water, possibly as a result of stabilization of suspended nanoparticles through interaction with dissolved organic carbon. Smaller nanoparticle aggregates appeared to preferentially adsorb to stream surfaces in turbulent sections, where Ce concentrations were highest in the press, likely a result of stochastic encounter with the surface. Streams receiving wastewater effluent containing nanoparticles may lead to exposure of aquatic organisms over a greater spatial extent than a similar amount of nanoparticles from an accidental release. Exposure models must take into account these mechanisms controlling transport and depositional processes.

Land use and topography as predictors of nitrogen levels in tropical catchments in Xishuangbanna, SW China

The conversion of vast tropical forests to cash crops represents a widespread land-use change in tropical regions, and has consequences for soil and water biogeochemical cycles. We examined how the conversion of tropical forest to rubber plantations in Xishuangbanna, southwest China, influenced the nitrogen concentrations in stream water. Water samples were collected between 2008 and 2010 at 35 sites to search for spatial and temporal variations in nitrogen concentrations and for their relationships with environment variables. Streams associated with rubber plantations (“rubber streams”) had significantly higher total N (TN) and total dissolved N (TDN) concentrations than forest streams during all seasons. TN, TDN and nitrate concentrations were observed to be significantly higher in streams associated with mixed land use than in forest streams only in the middle rainy season. The highest TN, TDN and nitrate concentrations were observed in rubber streams, and the lowest were observed in forest streams, indicating that land-use change had a significant effect on N concentrations. Statistically significant seasonal differences in TN, TDN and nitrate concentrations, with the greatest values in the middle rainy season, were observed in rubber and mixed streams, but not in forest streams. Canonical correspondence analysis identified the proportions of rubber plantation and tropical forest land, as well as slope gradient, as primary predictors of nitrogen concentration. Our results indicate that controlling rubber plantation expansion on steep slopes and avoiding single or large areas of rubber plantation within a catchment can mitigate nutrient loss.

A model to calculate effects of atmospheric deposition on soil acidification, eutrophication and carbon sequestration

Triggered by the steep decline in sulphur deposition in Europe and North America over the last decades, research and emission reduction policies have shifted from acidification to the effects of nitrogen (N) deposition and climate change on plant species diversity and carbon (C) sequestration in soils and biomass. Consequently, soil-ecosystem models need to include detailed descriptions of C and N processes, and ideally provide output that link to plant species diversity models. We describe an extension of the Very Simple Dynamic (VSD) model, called VSD+, which includes an explicit description of C and N turnover. Model simulations for three forest stands, which differ in N deposition and soil C/N ratios, show that VSD+ can well predict both trends and absolute values of NO3 and NH4 concentrations in soil and stream waters, soil C/N ratios and pH, which makes VSD+ suitable for providing input for plant species diversity models.

Effect of tourism-generated wastewater on biogenic ions concentrations in stream water in Tatra National Park (Poland)

The purpose of the research conducted in the years 2008–2009 was to determine the effect of wastewater generated by several tourist lodges in Tatra National Park (an alpine environment) on the concentration of biogenic ions (NH4 +, NO2 −, NO3 − and PO4 3−) in local streams into which the wastewater was being discharged. Wastewater discharged from mechanical biological wastewater treatment plants operated by tourist lodges usually has high concentrations of NH4 + and PO4 3−. The largest loads of biogenic ions were discharged into streams during the tourist season from May until September. Although the dilution conditions were good, the concentrations of some forms of biogenic ions in streams were significantly higher at points tens of metres downstream from the point of discharge than at points located upstream from the point of discharge. The concentrations of NH4 + and PO4 3− ions increased significantly in streams into which wastewater was being discharged from wastewater treatment plants in Tatra National Park (NP). Concentrations of NO3 − increased in the case of a stream into which untreated wastewater was being discharged after flowing down a mountain couloir for several hundred metres in the Tatras. The water and sewer management situation in Tatra NP has improved significantly since the time when this research was conducted. Poland’s entry into the European Union in 2005 made additional EU funding available to be invested in various environmental projects. Most existing wastewater treatment plants were fully modernized in the years 2010–2011, and new plants were built where none had been. Even so, it seems that transporting wastewater to treatment plants outside the national park is the most effective and reliable method of protecting the oligotrophic mountain waters of the Tatras from pollution.

Larval development of Culex quinquefasciatus in water with low to moderate.

Population growth and urbanization have increased the potential habitats, and consequently the abundance of Culex quinquefasciatus, the southern house mosquito, a vector of West Nile Virus in urban areas. Water quality is critical in larval habitat distribution and in providing microbial food resources for larvae. A mesocosm experiment was designed to demonstrate which specific components of water chemistry are conducive to larval Culex mosquitoes. Dose-response relationships between larval development and NO3 , NH4 , and PO4 concentrations in stream water were developed through this experiment to describe the isolated effects of each nutrient on pre-adult development. The emergence pattern of Culex mosquitoes was found to be strongly related to certain nutrients, and results showed that breeding sites with higher PO4 or NO3 concentrations had higher larval survival rates. High NO3 concentrations favor the development of male mosquitoes and suppress the development of female mosquitoes, but those adult females that do emerge develop faster in containers with high NO3 levels compared to the reference group. The addition of PO4 in the absence of nitrogen sources to the larval habitat slowed larval development, however, it took fewer days for larvae to reach the pupal stage in containers with combinations of NO3 and PO4 or NH4 and PO4 nutrients. Results from this study may bolster efforts to control WNV in urban landscapes by exploring water quality conditions of Culex larval habitats that produce adult mosquitoes.

Biophysical controls on dissolved organic carbon concentrations of Alaskan coastal temperate rainforest streams

Coastal carbon cycling models remain incomplete in key continental margins worldwide. Large quantities of labile terrestrial DOC are transferred to the Gulf of Alaska in a flow of freshwater discharge from thousands of watersheds that equals the discharge of the Mississippi River. The coastal margin of southeast Alaska and British Columbia is a potential hotspot of worldwide DOC metabolism and the mass and reactivity of DOC in rivers and estuaries of the region make quantifying and modeling DOC export a priority. Scaling DOC export requires a well-constrained model of streamwater DOC concentrations. We established models for prediction of DOC streamwater concentrations through a broad sampling of streams across a large, diverse landscape in 61 independent watersheds. Stream DOC concentrations were significantly related to the amount of wetlands in a watershed confirming the necessity of understanding the fate of the mass of carbon stored within them. Several measures of slope were useful in predictive models of streamwater DOC concentrations suggesting that slope predicts the presence of wetland soils better than current wetland map layers. We also provide evidence that suggests watersheds with large salmon spawning runs have distinct characteristics that influence the relationship between wetlands and carbon cycling that may provide additional insights into how carbon is processed.

Atmospheric Phosphorus and Nitrogen Originating in China: Forest Deposition and Infiltration of Stream Water in Japan

We analysed nutrients and basic ions (Na, Cl, K, Mg, Si, Ca, and SO4) for a period of 1 year, including every precipitation event, and sampled stream water every 2 weeks from a forest catchment in Shimane Prefecture, Japan. Backward-trajectory analysis revealed that some air masses originated within Japan, but did not affect the precipitation chemistry. Air masses originating from northern China were positively correlated with nutrients and all basic ions. Concentrations of ammonium and dissolved organic nitrogen were much lower in stream water than in precipitation, while those of nitrate and particulate nitrogen were similar in stream water and precipitation. Unlike nitrogen, the dissolved phosphorus concentration was much higher in stream water than in precipitation. Both phosphate and dissolved organic phosphorus (DOP) levels were higher in stream water than in precipitation. Particulate phosphorus (PP) concentrations were very similar in precipitation and stream water. PP showed stronger correlations than potassium with suspended solids (SS) and flow rate, while phosphate and DOP were more strongly correlated with potassium than with SS or flow rate. Stream silica concentrations were not correlated with phosphate but did exhibit a significant negative correlation with DOP. Neither phosphate nor DOP was correlated with calcium. These results suggest that phosphorus is not leaching with silica or calcium as a paired cation, but rather with potassium in this area. Lower nitrogen concentrations in stream water than in precipitation can be attributed to an enhanced uptake of nitrogen by forest soils owing to the increased atmospheric deposition of phosphorus.

Use of a geographic information system (GIS) for targeting radon screening programs in South Dakota.

Because 222Rn is a progeny of 238U, the relative abundance of uranium may be used to predict the areas that have the potential for high indoor radon concentration and therefore determine the best areas to conduct future surveys. Geographic Information System (GIS) mapping software was used to construct maps of South Dakota that included levels of uranium concentrations in soil and stream water and uranium deposits. Maps of existing populations and the types of land were also generated. Existing data about average indoor radon levels by county taken from a databank were included for consideration. Although the soil and stream data and existing recorded average indoor radon levels were sparse, it was determined that the most likely locations of elevated indoor radon would be in the northwest and southwest corners of the state. Indoor radon levels were only available for 9 out of 66 counties in South Dakota. This sparcity of data precluded a study of correlation of radon to geological features, but further motivates the need for more testing in the state. Only actual measurements should be used to determine levels of indoor radon because of the strong roles home construction and localized geology play in radon concentration. However, the data visualization method demonstrated here is potentially useful for directing resources relating to radon screening campaigns.

Watershed features and stream water quality: Gaining insight through path analysis in a Midwest urban landscape, U.S.A.

Urban stream condition is often degraded by human activities in the surrounding watershed. Given the complexity of urban areas, relationships among variables that cause stream degradation can be difficult to isolate. We examined factors affecting stream condition by evaluating social, terrestrial, stream hydrology and water quality variables from 20 urban stream watersheds in central Iowa, U.S.A. We used path analysis to examine and quantify social and ecological factors related to variation in stream conditions. Path models supported hypotheses that stream water quality was influenced by variables in each category. Specifically, one path model indicated that increased stream water conductivity was linked to high road density, which itself was associated with high human population density. A second path model revealed nitrogen concentration in stream water was positively related to watershed area covered by cropland, and that cropland increased as human population density declined. A third path model indicated phosphorus concentration in stream water declined as percent of watershed residents with college education increased, although the mechanism underlying this relationship was unclear and could have been an artifact of lower soil-derived nutrient input from watersheds dominated by paved surfaces. To improve environmental conditions in urban streams, land use planning strategies should include limiting or reducing road density near streams, installing treatment trains for surface water runoff associated with roads, and establishing vegetated buffer zones to reduce inputs of road salt and other pollutants. Additionally, education/outreach should be conducted with residents to increase understanding of how their own behaviors influence stream water quality.

Landscape heterogeneity drives contrasting concentration–discharge relationships in shale headwater catchments

Abstract. Solute concentrations in stream water vary with discharge in patterns that record complex feedbacks between hydrologic and biogeochemical processes. In a comparison of three shale-underlain headwater catchments located in Pennsylvania, USA (the forested Shale Hills Critical Zone Observatory), and Wales, UK (the peatland-dominated Upper Hafren and forest-dominated Upper Hore catchments in the Plynlimon forest), dissimilar concentration–discharge (C–Q) behaviors are best explained by contrasting landscape distributions of soil solution chemistry – especially dissolved organic carbon (DOC) – that have been established by patterns of vegetation and soil organic matter (SOM). Specifically, elements that are concentrated in organic-rich soils due to biotic cycling (Mn, Ca, K) or that form strong complexes with DOC (Fe, Al) are spatially heterogeneous in pore waters because organic matter is heterogeneously distributed across the catchments. These solutes exhibit non-chemostatic behavior in the streams, and solute concentrations either decrease (Shale Hills) or increase (Plynlimon) with increasing discharge. In contrast, solutes that are concentrated in soil minerals and form only weak complexes with DOC (Na, Mg, Si) are spatially homogeneous in pore waters across each catchment. These solutes are chemostatic in that their stream concentrations vary little with stream discharge, likely because these solutes are released quickly from exchange sites in the soils during rainfall events. Furthermore, concentration–discharge relationships of non-chemostatic solutes changed following tree harvest in the Upper Hore catchment in Plynlimon, while no changes were observed for chemostatic solutes, underscoring the role of vegetation in regulating the concentrations of certain elements in the stream. These results indicate that differences in the hydrologic connectivity of organic-rich soils to the stream drive differences in concentration behavior between catchments. As such, in catchments where SOM is dominantly in lowlands (e.g., Shale Hills), we infer that non-chemostatic elements associated with organic matter are released to the stream early during rainfall events, whereas in catchments where SOM is dominantly in uplands (e.g., Plynlimon), these non-chemostatic elements are released later during rainfall events. The distribution of SOM across the landscape is thus a key component for predictive models of solute transport in headwater catchments.

Particulate nitrogen exports in stream runoff exceed dissolved nitrogen forms during large tropical storms in a temperate, headwater, forested watershed

AbstractAlthough lasting only a fraction of the year, large storms may represent a significant, but highly variable, control on watershed nitrogen (N) fluxes. We determined the exports of particulate N (PN) and total dissolved N including nitrate‐N (NO3‐N) and dissolved organic N (DON) in streamflow from a 12 ha temperate forested watershed. Sampling was performed for 15 storms over September 2010 to December 2012 and included four large tropical storms—Nicole (2010), Irene and Lee (2011), and Sandy (2012). PN composed a substantial portion (39–87%) of the storm event N export with storms constituting 65% of the 2011 PN export. Tropical storm Irene alone generated 1.76 kg N ha−1 of PN which was 27% of the annual watershed N (6.43 kg N ha−1) export for 2011. In contrast, tropical storm Sandy (October 2012) yielded low sediment and PN exports, likely due to low precipitation intensity and a freshly fallen leaf cover that may have reduced soil erosion. Stream water concentrations of PN, NO3‐N, and DON ranged from 0–17.5, 0–2.02, and 0.01–0.54 mg N L−1, respectively. Nitrate‐N concentrations displayed a dilution trajectory for peak stormflows suggesting supply limitation, a response that was not as strong for PN. These results underscore the importance of large storms for PN export which is significant given that climate‐change predictions indicate an increasing intensity of large tropical storms for the northeast U.S.. Elevated PN exports could further exacerbate water quality and eutrophication problems in sensitive aquatic ecosystems already subjected to excess dissolved nitrogen loads.

Application of D-SEM to a catchment in Central Amazonia: calibration and validation of the carbon and nitrogen cycles

We applied the D-SEM model for predicting carbon (C) and nitrogen (N) dynamics in a natural forest ecosystem in a Central Amazonian microcatchment. A continuous collection of hydrological and water quality data (2002–2010) was used for model calibration and validation. Comparisons between predicted and measured hydrologic variables showed that the model captured seasonal and interannual discharges and DOC concentrations in stream water. The model also reproduced the monthly dynamics of DOC in the soil pool and captured seasonal changes in nitrogen transformations following seasonal variations in rainfall, including increased mineralization, nitrification, lixiviation, and decreased denitrification. Model estimates of monthly DON and NH4 in stream water concentration were comparable to measured values (0.37±0.22; 0.065±0.06, respectively). Overall, this study demonstrated that the D-SEM model can predict water, C and N dynamics in drained forests under natural conditions in the Amazon. However, discrepancies between the magnitudes of the estimates suggest that the model requires refinement for further application in tropical forested catchments.

Acute Toxicity of Endosulfan to the Non-target Organisms Hyalella curvispina and Cnesterodon decemmaculatus.

Pesticide consumption in Argentina has steadily increased over the last two decades, while one of these compounds, namely endosulfan, is commonly found in environmental samples. Also the fish Cnesterodon decemmaculatus and the amphipod Hyalella curvispina are widely distributed in agricultural areas of southern South America. The aim of the present contribution was therefore to determine the acute toxicity of endosulfan to both organisms, and compare it with species sensitivity distributions (SSD) and measured field concentrations. The 48 h-LC50 (with 95 % confidence limits) were 1.8 (1.6-2.1) µg/L for C. decemmaculatus and 16.4 (15.1-17.7) µg/L for H. curvispina. C. decemmaculatus was more sensitive than 74 % of fish based on the SSD. Endosulfan concentrations in stream water reported in the literature were often higher than the C. decemmaculatus LC50. It may hence be concluded that C. decemmaculatus is a suitable sentinel organism for ecotoxicological risk assessment in South America.

Influence of strip thinning on nutrient outflow concentrations from plantation forested watersheds

AbstractNutrient concentrations in stream water, rainfall, throughfall, stemflow, surface flow and ground water were compared before, during and after strip thinning (intensive 50%) in plantation forested watersheds in Tochigi, Japan. Influences were evaluated comparing four thinning‐applied and two reference basins for 1 year before, 6 months during and 1 year after the thinning. Results show that this strip thinning significantly increased dissolved total phosphorus, total phosphorus and dissolved organic carbon (0.01, 0.04 and 0.53 mg l−1, respectively) during the thinning period and dissolved total nitrogen and total nitrogen (0.34 and 0.46 mg l−1, respectively) after the thinning in stream waters relative to the unthinned basins. The increased phosphorus during thinning indicated ground disturbances by the strip thinning, with a concomitant increase in dissolved organic carbon. Changes in biotic and abiotic conditions resulted in increased nitrogen after the thinning, particularly in the dissolved pool. Changes in hydrological processes due to thinning, for example, a change in flow distributions (less high nutrient stemflow and more low nutrient throughfall) and an increase in water discharge in stream water, possibly weakened the direct influences of thinning on nutrient concentrations. Copyright © 2015 John Wiley &amp; Sons, Ltd.