Weathering fluxes of arsenic from a small catchment in Slovak Republic

Inputs of As to a small catchment due to chemical weathering of bedrock, mechanical weathering of bedrock, and atmospheric precipitation were 71.53, 23.98 and 0.02 g ha⁻¹ year⁻¹, respectively. The output fluxes of As due to mechanical erosion of soil, biological uptake, stream discharge, and groundwater flow were 6.32, 4.77, 0.37 and 0.02 g ha⁻¹ year⁻¹, respectively. The results indicate that arsenic accumulates in soil and regolith with a very high rate. This is attributed to the selective weathering and erosion with respect to arsenic and fixation of arsenic in the secondary solids produced by weathering. The output fluxes of As in stream and groundwater in Vydrica catchment in Slovak Republic (0.39 g ha⁻¹ year⁻¹) based on muscovite–biotite granites and granodiorites were much lower compared to catchments in a gold district in the Czech Republic. These results may be ascribed to the low levels of arsenic pollution measured in Vydrica catchment. The arsenic fluxes were estimated by calculation of mechanical and chemical weathering rates of the bedrocks in Vydrica catchment from mass balance data on sodium and silica. The justification of the steady state of Na and Si is that neither of the elements is appreciably accumulated in plants and in exchangeable pool of ions in soil.     

Soil erosion risk assessment of the Keiskamma catchment,South Africa using GIS and remote sensing

This paper examines the soil loss spatial patterns in the Keiskamma catchment using the GIS-based Sediment Assessment Tool for Effective Erosion Control (SATEEC) to assess the soil erosion risk of the catchment. SATEEC estimates soil loss and sediment yield within river catchments using the Revised Universal Soil Loss Equation (RUSLE) and a spatially distributed sediment delivery ratio. Vegetation cover in protected areas has a significant effect in curtailing soil loss. The effect of rainfall was noted as two pronged, higher rainfall amounts received in the escarpment promote vegetation growth and vigour in the Amatole mountain range which in turn positively provides a protective cover to shield the soil from soil loss. The negative aspect of high rainfall is that it increases the rainfall erosivity. The Keiskamma catchment is predisposed to excessive rates of soil loss due to high soil erodibility, steep slopes, poor conservation practices and low vegetation cover. This soil erosion risk assessment shows that 35% of the catchment is prone to high to extremely high soil losses higher than 25 ton ha⁻¹ year⁻¹ whilst 65% still experience very low to moderate levels of soil loss of less than 25 ton ha⁻¹ year⁻¹. Object based classification highlighted the occurrence of enriched valley infill which flourishes in sediment laden ephemeral stream channels. This occurrence increases gully erosion due to overgrazing within ephemeral stream channels. Measures to curb further degradation in the catchment should thrive to strengthen the role of local institutions in controlling conservation practice.     

Setting load limits for nutrients and suspended solids based upon seagrass depth-limit targets

Total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) loadings [log (kg ha⁻¹ yr⁻¹)] were regressed against seagrass depth limits (percent of depth-limit targets) to back-predict the load limits or allocations (kg ha⁻¹ yr⁻¹ or kg yr⁻¹) necessary to meet targeted seagrass depth limits in the Indian River and Banana River (IRBR) lagoons, Florida. Because the load allocations can be applied as total maximum daily loads (TMDL) for the IRBR (U.S. Environmental Protection Agency mandate), the method and results are developed and presented toward that end. The regression analyses indicate that the range of surface-discharge load limits (nonpoint + point source), per watershed area, required to achieve the desired depth limits for seagrass in the IRBR are approximately 2.4–3.2 kg ha⁻¹ yr⁻¹ TN, 0.41–0.64 kg ha⁻¹ yr⁻¹ TP, and 48–64 kg ha⁻¹ yr⁻¹ TSS. This simple regression method may have application to other shallow estuarine lagoons or bays where seagrass growth is limited by light and water transparency, water transparency is strongly affected by watershed pollutant loadings, water residence times are sufficiently long to allow seagrass coverage to respond to and covary with total load inputs, and multiyear monitoring has yielded sufficient variability in both pollutant loadings and seagrass coverages to develop a statistically meaningful relationship.     

洪湖流域传统农业条件下营养盐输移模拟研究*

文章选择位于长江中游的洪湖流域作为研究对象,应用流域分布式水文模型SWAT,探讨传统农业条件下流域营养盐输移的规律。模拟时段选择为建国初期的1951~1960年,模拟的边界条件设置为自然地形、土壤、传统农业生产和土地利用方式,其中土壤资料包括营养盐(N和P)、有机质含量、粒径等理化参数等。根据流域汇水范围的变化,模拟分汛期与非汛期两个时间段进行。通过对模型参数率定和调试,水文模拟结果与实测值有较好的吻合程度,由此进行营养盐输出模拟。模拟结果显示,传统农业条件下流域营养盐输出,TN和TP浓度变化有明显的季节特征,体现了耕作制度对营养盐浓度的影响; 同时,该时段营养盐浓度相比较自然条件下有了很大的改变,体现了人类活动对流域营养盐输移的影响,主要是土地利用类型变化和湖泊水域面积的缩小。     

Soil erosion determinations by using 137Cs technique in the agricultural regions of Gediz Basin, Western Turkey

Gediz Basin is one of the regions where intense agricultural activities take place in Western Turkey. Erosion and soil degradation have long been causing serious problems to cultivated fields in the basin. This work describes the application of two different ¹³⁷Cs models for estimating soil erosion rates in cultivated sites of the region. Soil samples were collected from five distinct cultivated regions subject to soil erosion. The variations of ¹³⁷Cs concentrations with depth in soil profiles were investigated. Soil loss rates were calculated from ¹³⁷Cs inventories of the samples using both proportional model (PM) and simplified mass balance model (SMBM). When PM was used, erosion and deposition rates varied from −15 to −28 t ha⁻¹ year⁻¹ and from +5 to +41 t ha⁻¹ year⁻¹, respectively; they varied from −16 to −33 t ha⁻¹ year⁻¹ and from +5 to +55 t ha⁻¹ year⁻¹ with SMBM. A good agreement was observed between the results of two models up to 30 t ha⁻¹ year⁻¹ soil loss and gain in the study area. Ulukent, a small representative agricultural field, was selected to compare the present data of ¹³⁷Cs techniques with the results obtained by universal soil loss equation (USLE) applied in the area before.     

Erosion rates evaluated by the <Superscript>137</Superscript>Cs technique in the high altitude area of the Qinghai–Tibet plateau of China

Studying spatial and temporal variation of soil loss is of great importance because of global environmental concerns. Understanding the spatial distribution of soil erosion and deposition in the high-cold steppe is important for designing soil and water conservation measures. Measured ¹³⁷Cs losses (Bq m⁻²) from long-term high altitude (4,000 m above sea level) watershed plots on the Qinghai–Tibet plateau and derived soil erosion estimates (Mg ha⁻¹ year⁻¹) were significantly correlated to directly measured soil losses from the same plots, over the same period (1963–2005). The local reference inventory was estimated to be 2,468 Bq m⁻². The result of analyzing ¹³⁷Cs distribution and its intensity in the soil profiles in this area shows similarities to ¹³⁷Cs distribution in other areas. ¹³⁷Cs is basically distributed in the topsoil layer of 0–0.3 m. Soil erosions vary greatly in the entire sampled area, ranging from 5.5 to 23 Mg ha⁻¹ year⁻¹, with an average of 16.5 Mg ha⁻¹ year⁻¹ which is a moderate rate of erosion.     

Sources of nitrogen to estuaries in the United States

The purpose of this study was to quantify the nitrogen (N) inputs to 34 estuaries on the Atlantic and Gulf Coasts of the United States. Total nitrogen (TN) inputs ranged from 1 kg N ha⁻¹ yr⁻¹ for Upper Laguna Madre, Texas, to 49 kg N ha⁻¹ yr⁻¹ for Massachusetts Bay, Massachusetts. TN inputs to 11 of the 34 estuaries were dominated by urban N sources (point sources and septic systems) and nonpoint source N runoff (5% of total); point sources accounted for 36–86% of the TN inputs to these 11 urban-dominated estuaries. TN inputs to 20 of the 34 estuaries were dominated by agricultural N sources; N fertilization was the dominant source (46% of the total), followed by manure (32% of the total) and N fixation by crops (16% of the total). Atmospheric deposition (runoff from watershed plus direct deposition to the surface of the estuary) was the dominant N source for three estuaries (Barnegat Bay, New Jersey: 64%; St. Catherines-Sapelo, Georgia: 72%; and Barataria Bay, Louisiana: 53%). Six estuaries had atmospheric contributions ≥30% of the TN inputs (Casco Bay, Maine: 43%; Buzzards Bay, Massachusetts: 30%; Great Bay, New Jersey: 40%; Chesapeake Bay: 30%; Terrebonne-Timbalier Bay, Louisiana: 59%; and Upper Laguna Madre: 41%). Results from our study suggest that reductions in N loadings to estuaries should be accomplished by implementing watershed specific programs that target the dominant N sources.     

Arsenic in the groundwater of Ouro Preto (Brazil): its temporal behavior as influenced by the hydric regime and hydrogeology

In the city of Ouro Preto (MG), water catchment for public supply originates from superficial drainage, springs, old abandoned mines and some driven wells. In the rocks of the region, As is originally found in gold-enriched sulphide-bearing mineral deposits. The weathering process introduces As into the hydrological system by dissolution of this element into the leachate. Measurement of the As content in the groundwater of some catchments was carried out during 1 year and these measurements demonstrated high As content—up to 224 μg L⁻¹ of As(V)—during the rainy season (the maximum concentration limit according to World Health Organization is 10 μg L⁻¹). Lower values were observed during the dry season and in some sampling stations, As was not even detected. The As concentration variability during 1 year shows a strict and direct relationship to seasonal and hydrological conditions. For city authorities, responsible for public water supply, it is necessary to perform a complete inventory of the water sources used and constantly monitor the As content in the water.     

Assessment of present and future nitrogen loads, water quality, and seagrass (Thalassia testudinum) depth distribution in Lemon Bay, Florida

Nitrogen loads into Lemon Bay, Florida were modeled to have increased ca. 59% between pre-development (i.e., 1850) estimates (5.3 kg TN ha⁻¹ yr⁻¹. and estimates for the year 1995 (8.4 kg TN ha⁻¹ yr⁻¹). By the year 2010, nitrogen loads are predicted to increase an additional 45% or 58%, depending upon progress being made toward replacing older septic tank systems with centralized sewerage (nitrogen loads of 12.2 and 13.3 kg TN ha⁻¹ yr⁻¹, respectively). Using 1995 estimates, nonpoint sources (stormwater runoff) are throught to be responsible for ca. 76% of the annual nitrogen load, followed by septic tank systems (14%), rainfall (10%), and an insignificant load from baseflow. Based on an empirically-derived nitrogen load:chlorophylla relationship developed for a portion of nearby Tampa Bay, a 45% increase in nitrogen loads into Lemon Bay could result in a 29% increase in annual average chlorophylla concentrations. Using the estimate of a 29% increase in future chlorophylla concentrations, an empirically-derived optical model for Lemon Bay suggests that light attenuation coefficients in the bay would increase ca. 9%, and the average depth limit ofThalassia testudinum in Lemon Bay would decrease by ca. 24%.     

Characteristics of Non—Point Source Pollution in the Watershed of Miyun Reservoir,Beijing,China

Nitrogen and phosphorus are the major nutrients to cause eutrophication to degrade water quality of the Miyun Reservoir,a very important drinking water source of Bijing,China,and they are mainly from non-point sources.The watershed in Miyun County was selected as the study region with a totoal area of 1400km^2.Four typical monitoring catchments and two experimental units were used to monitor the precipitation,runoff,sediment yield and pollutant loading related to various land uses in the meantime.The results show that the total nutrient loss amounts of TN and TP are 898.07t/a,and 40.70t/a,respectively,in which nutrients N and P carried by runoff are 91.3% and 77.3%,respectively.There is relatively heavier soil eroson in the northern mountain area whereas the main nutrient loss occurs near the northeast edge of the reservoir.Different land uses would influence the loss amounts of non-point source pollutants.The amount of nutrient loss from the agricultural land per unit is highest,that from forestry comes next that from grassland is lowest.However,due to the variability of land use areas,agricultural land contributes a lot to TP and forestry lands to TN.     

Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia,China

Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha⁻¹ year⁻¹; MN, 100 kg N ha⁻¹ year⁻¹; LN, 50 kg N ha⁻¹ year⁻¹) on soil respiration compared with non-fertilization (CK, 0 kg N ha⁻¹ year⁻¹), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments (Q ₁₀ varied within 1.70–1.74) but was slightly reduced in MN treatment (Q ₁₀ = 1.63). N fertilization increased soil CO₂ emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN and MN (P < 0.05) and reached a marginally significant level for LN (P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July–September 2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007–June 2008). The annual total soil respiration was 53, 57, and 24% higher than in the CK plots (465 g m⁻² year⁻¹). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July–September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year (P > 0.05).     

Modeling runoff and soil erosion in a catchment area, using the GIS, in the Himalayan region, India

Remote sensing data and GIS techniques have been used to compute runoff and soil erosion in the catchment area along the NH-1A between Udhampur and Kud covering an area of approximately 181 km². Different thematic layers, for example lithology, a landuse and landcover map, geomorphology, a slope map, and a soil-texture map, were generated from these input data. By use of the US Soil Conservation Service curve number method, estimated runoff potential was classified into five levels—very low, low, moderate, high, and very high. Data integration was performed by use of the weighting rating technique, a conventional qualitative method, to give a runoff potential index value. The runoff potential index values were used to delineate the runoff potential zones, namely low, moderate, high, and very high. Annual spatial soil loss estimation was computed using the Morgan–Morgan–Finney mathematical model in conjunction with remote sensing data and GIS techniques. Greater soil erosion was found to occur in the northwestern part of the catchment area. When average soil loss from the catchment area was calculated it was found that a maximum average soil loss of more than 20 t ha⁻¹ occurred in 31 km² of the catchment area.     

Utilizing the MODIS-derived leaf area index to investigate the impact of vegetation processes on hydrological simulation of macroscale catchment

Integration of vegetation processes in rain–runoff (RR) models significantly affects runoff response by influencing evapotranspiration in mesoscale catchments. However, it is impossible to interpret the impacts of vegetation processes on runoff simulations in macroscale catchments using results from mesoscale catchments. Few studies involved vegetation process impacts on hydrological simulations by integrating daily vegetation information into conceptual RR models of macroscale catchments. In this study, we integrated the remotely sensed leaf area index (LAI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) into a daily Distributed Time-Variant Gain Model (DTVGM). Then, this study assessed the performances of two DTVGM versions, with and without vegetation processes, in the Wei River catchment, China. The results showed that: (1) Integration of MODIS-LAI into the DTVGM model improved the calibration and runoff simulation results of the initial DTVGM model. (2) Inclusion of vegetation processes in the DTVGM changed the simulated proportions of water balance components in the hydrological model and made the simulation of water balance components more accurate. (3) The fact that inclusion of vegetation processes could improve the hydrological simulation performance of the daily conceptual RR model in the macroscale catchment was consistent with studies in mesoscale catchment.     

Short-term variability of water quality parameters in two shallow estuaries of North Carolina

We quantified the effects of nutrient loading following precipitation events (≥ 1.25 cm) in 2 tidal creeks varying in size and anthropogenic input during the winter and summer seasons of 1996. Several water quality parameters were repeatedly measured in the water column every 3 h for several days after each event (4–5 per season). Total nitrogen (TN) and total phosphorus (TP) behaved nonconservatively with salinity and appeared as pulsed additions, occasionally doubling within 1 to 2 tidal cycles following significant rain events. Average values for TN, TP, and chlorophylla were 10–15 μM, <4 μM, and <7 μg l⁻¹, respectively for winter events and 30–35 μM, >4 μM, and ≥ 7 μg l⁻¹, respectively for summer events. However, response times were variable, depending on the magnitude and duration of the event as well as temperature. Chlorophylla biomass often increased after nutrient additions, especially in the summer when increased nutrient loading took place. Dissolved silica (DSi) behaved conservatively with salinity; low values were observed at high tide and vice versa. Average DSi ranges for winter and summer events were 5–45 μM and 10–85 μM, respectively. DSi range values increased proportionally with the amount of freshwater loaded into the system. Recovery times for salinity were usually greater than the recovery times for nutrients. Dissolved oxygen displayed a diel pattern, increasing after daytime productivity and decreasing during nighttime. In conclusion, each rainfall event was unique and responses were variable depending upon rainfall history, seasonality, and the duration and intensity of the rainfall event. Several other variables, such as water viscosity, percolation rates, and evapotranspiration rates which were not quantified in this study, could have also explained parameter responses.     

Mapping of total nitrogen,available phosphorous and potassium in Amik Plain,Turkey

Soil nitrogen, phosphorous, and potassium concentrations accurately revealed spatial distribution maps and site-specific management-prone areas through inverse distance weighting (IDW) method in the Amik Plain, Turkey. Spatial mapping of soil nitrogen, phosphorous, and potassium is a very severe need to develop an economically and environmentally sound soil management plans. The objectives of this study were (a) to map spatial variability of total N, available P, and exchangeable-K content of Amik Plain’s soils and (b) to locate problematic areas requiring site specific management strategies for the nutrient elements. Spatial analyses of Kjeldhal-N, Olsen-P, and exchangeable-K concentrations of the soils were performed by the IDW method. Mean N content for surface soils (0–20 cm) was 1.38 g kg⁻¹, available P was 28.19 kg ha⁻¹ and exchangeable-K was 690 kg ha⁻¹ with the differences between maximum and minimum being 7.63 g N kg⁻¹, 242 kg P ha⁻¹, and 2,082 kg K ha⁻¹. For the surface soil, site-specific management-prone areas of Kjeldahl-N, Olsen-P, and exchangeable-K for “low and high + very high” classes were found to be 20.1–17.8%, 24.7–10.0%, and 4.1–39.6%, respectively. Consequently, lands with excessive nutrient elements require preventive-leaching practices, whereas nutrient-poor areas need fertilizer applications in favor of increasing plant production.     

Whole Ecosystem Evidence of Eutrophication Enhancement by Wetland Dredging in a Shallow Tropical Lake

The purpose of this research was to assess the effects of dredging performed in a marginal wetland colonized by aquatic macrophytes on eutrophication of the adjacent shallow tropical lake (Imboassica Lake, Brazil). The river mouth of the Imboassica River that drains into Imboassica Lake had been densely colonized by aquatic vegetation dominated by Typha domingensis (Pers.) when it was dredged. Total and dissolved nitrogen and phosphorus concentrations were measured monthly over 13 years at four stations in the Imboassica river-lake system. Dredging activities reduced phosphorus and nitrogen retention at the river mouth and subsequently increased these nutrient stocks in the lake waters. Nutrient retention by non-dredged wetland was estimated to be ca. 1,200 kg year⁻¹ (87.3 g m⁻² year⁻¹) for nitrogen and 60 kg year⁻¹ (4.5 g m⁻² year⁻¹) for phosphorus. Our whole-lake approach suggested that dredging might intensify rather than mitigate eutrophication in shallow tropical lakes when the removal of aquatic macrophytes is coupled to the persistence of anthropogenic nutrient inputs from the watershed.     

太湖流域营养盐产量演变和趋势的数值模拟研究

认识流域湖泊水体富营养化的演变和趋势是湖泊污染控制和治理中的重要研究课题。本文将在分析和论证太湖流域营养盐自然本底、人类活动作用急剧增加的近50年来太湖流域营养盐的变化情况、以及全球气候变化和流域经济发展未来30年太湖流域营养盐变化趋势等三方面的基础上,对太湖流域营养盐产量变化做出评估和预测。研究表明,在未来气候变化概率分析和区域经济发展规划基础上,太湖流域未来30年营养盐流域产量将比现代（2000s）增加25%～33%,这将增大太湖水体污染的压力。     

Quantifying Annual Nitrogen Loads to Virginia’s Coastal Lagoons: Sources and Water Quality Response

Coastal lagoons of the Delmarva Peninsula receive varying annual nitrogen loads because of differing land uses. Extensive development and agriculture contribute to elevated nutrient loads in Maryland and Delaware. Agriculture and forests dominate Virginia’s landscape, suggesting these systems receive lower loads. We used a watershed model to achieve three objectives: (1) quantify loads to Virginia lagoons; (2) determine the sources of the loads; and (3) project changes in annual loads under different development scenarios. Model simulations indicated that some Virginia lagoons receive relatively high annual nutrient loads (kg N year⁻¹) due to intensive agriculture and a high watershed/lagoon areal ratio. Model projections also suggested that increased agricultural and residential development in Virginia could lead to annual loads (kg N year⁻¹) typical of impacted Maryland systems. A comparison of Maryland and Virginia water quality responses to nutrient loading suggested that Virginia’s lagoons exhibit a different response to nutrient loading, though the exact mechanism for this difference is unclear.     

<Superscript>210</Superscript>Pb-derived Sedimentation Rates and C<Subscript>org</Subscript> Fluxes in Soledad Lagoon (Cispatá Lagoon System,NW Caribbean Coast of Colombia)

With the aim of evaluating temporal changes in sedimentation and organic carbon (C_org) supplied over the last ~100 years, a sediment core was collected at Soledad Lagoon, a costal ecosystem surrounded by mangroves, located in the Cispatá Estuary (Caribbean coast of Colombia). The core sediments were characterized by low concentrations of calcium carbonate (0.2–2.9%), organic matter (3–8%), total nitrogen (0.11–0.38%), and total phosphorus (0.19–0.65 mg g⁻¹). Fe and Al concentrations ranged from 4% to 5%, and Mn from 356 to 1,047 μg g⁻¹. The ²¹⁰Pb-derived sediment and mass accumulation rates were 1.54 ± 0.18 mm year⁻¹ and 0.08 ± 0.01 g cm⁻² year⁻¹, respectively. The sediment core did not provide evidence of human impact, such as enhancement of primary production or nutrient enrichment, which may result from recent land uses changes or climate change. The C_org fluxes estimated for Soledad Lagoon core lay in the higher side of carbon fluxes to coastal ecosystems (314–409 g m⁻² year⁻¹) and the relatively high C_org preservation observed (~45%) indicate that these lagoon sediments has been a net and efficient sink of C_org during the last century, which corroborate the importance of mangrove areas as important sites for carbon burial and therefore, long-term sequestration of C_org.