Effects of changing land use on the microbial water quality of tidal creeks

Population growth along the southeastern United States coast has precipitated the conversion of forested watersheds to suburban and urban ones. This study sampled creeks representing forested, suburban, and urban watersheds along a longitudinal gradient for indicators of water quality, including traditional indicator bacteria (fecal coliforms and enterococci) and alternative viral indicators (male-specific and somatic coliphages). Tested microorganisms were generally distributed with highest concentrations in creek headwaters and in more developed watersheds. The headwaters also showed the strongest predictive relationship between indicator concentrations and urbanization as measured by impervious cover. A seasonal pattern was observed for indicator bacteria but not for indicator viruses. Coliphage typing indicated the likely source of contamination was nonhuman. Results suggest that headwater creeks can serve as sentinel habitat, signaling early warning of public health concerns from land-based anthropogenic activities. This study also implies the potential to eventually forecast indicator concentrations under land use change scenarios.     

Effects of geomorphology and land use on stream water quality in southeastern Amazonia

Water quality in streams is determined by several factors, including geology, topography, climate, and anthropogenic changes. This study aimed to assess the effects of watershed physical, morphology, and precipitation seasonality on the water quality of two streams that supply drinking water to rural settlements and urban areas in the Cerrado-Amazonia transition region. We monitored 16 physico-chemical attributes of water at six different sample locations over three years (2013–2016). Our results indicate that eight of these physico-chemical attributes did not meet the standards for safe drinking water established by Brazilian legislation. Precipitation seasonality, degradation of riparian zones, stream length, and watershed slope were the most important predictors of impaired water quality. Our results highlight the importance of restoring and conserving riparian forests in order to maintain drinking water quality.     

Predicting ground water nitrate concentration from land use

Ground water nitrate concentrations on Nantucket Island, Massachusetts, were analyzed to assess the effects of land use on ground water quality. Exploratory data analysis was applied to historic ground water nitrate concentrations to determine spatial and temporal trends. Maximum likelihood Tobit and logistic regression analyses of explanatory variables that characterize land use within a 1000-foot radius of each well were used to develop predictive equations for nitrate concentration at 69 wells. The results demonstrate that historic nitrate concentrations downgradient from agricultural land are significantly higher than nitrate concentrations elsewhere. Tobit regression results demonstrate that the number of septic tanks and the percentages of forest, undeveloped, and high-density residential land within a 1000-foot radius of a well are reliable predictors of nitrate concentration in ground water. Similarly, logistic regression revealed that the percentages of forest, undeveloped, and low-density residential land are good indicators of ground water nitrate concentration > 2 mg/L. The methodology and results outlined here provide a useful tool for land managers in communities with shallow water tables overlain with highly permeable materials to evaluate potential effects of development on ground water quality.     

The impact of land use on stream water quality in Slovakia

In the first part of this paper, the impact of forestry, agriculture and urban activities on the quality of surface water is analysed. Daily data from 15 forest and agricultural experimental catchments of the Institute of Hydrology, Slovak Academy of Sciences are used. It is shown, that the nitrate concentrations in surface water have decreased in Slovakia since 1989 as a result of decreased use of inorganic nitrogen fertilisers (lower intensity of agricultural production in Slovakia owing to recent economic changes). The annual nitrate specific load varies from 5.90 to 110 kg ha⁻¹ year⁻¹, the annual sulphate load varied from 29.16 to 509.60 kg ha⁻¹ year⁻¹ and the annual phosphate load varied from 0.0098 to 0.0224 kg ha⁻¹ year⁻¹ during 1990–1992.

In the second part, a two-step method of three-component hydrograph separation of rain-, soil- and groundwater is proposed. The method is used in the Manelo-Gribov microbasin (O.95 km²) in Eastern Slovakia. The annual contribution of surface runoff in total runoff volume was 57.5%, the contribution of interflow runoff was 21.1%, and the contribution of groundwater was 21.4%, during the period from 1 August to 31 July 1992. A deterministic regression model for predicting daily nitrate concentrations from values of stream daily discharge and flow component data was developed. A set of 1421 modelled NO₃⁻¹ data was compared with the set of measured data.     

山地城市河流土地利用结构对水质的影响--以重庆市为例

以重庆主城区6条次级河流为研究区域,运用遥感和地理信息系统计算研究区土地利用构成,借助相关性分析和冗余分析等数理统计手段,分析监测断面汇水区内不同尺度土地利用结构与水质指标间的相关关系.结果表明:研究区土地利用结构以建设用地和林地为主,未利用地和农业用地所占面积比例较少;研究区土地利用结构对各水质指标有重要影响,其中建设用地和农业用地对河流水质恶化具有明显的作用,河流沿岸林地布局能显著改善水质,但随着雨季的到来林地将成为硝态氮的来源.冗余分析进一步证实土地利用类型对水环境有一定影响.研究成果对重庆市河流水环境管理具有重要的实际指导意义,并可为山地城市河流水环境研究提供借鉴.     

Riparian land use and stream habitat regulate water quality

Riparian land use is a key driver of stream ecosystem processes but its effects on water quality are still a matter of debate when proposing measures to improve freshwater quality. The aim of this study was to examine the influence of riparian land use on stream habitat and water chemistry, and to assess in what extent stream habitat also affects water quality. To that end, we selected eight reaches in the Ave River basin (northwestern Portugal) and compared longitudinal variations in water chemistry and stream habitat between reaches with different land use (urban, agricultural and natural), and between reaches with natural riparian areas and different habitats. Stream habitat was assessed using the Fluvial Functional Index, the HABSCORE, and the Riparian Forest Quality Index. Longitudinal variations in water chemistry were determined measuring differences in concentrations of ammonium, nitrate, phosphate and oxygen, and conductivity, pH and temperature between the downstream and the upstream ends of each reach. Nitrate concentration tended to decrease along reaches with more natural riparian areas and to increase along reaches with more urban and agricultural land uses. Longitudinal variations in water chemistry also differed between reaches with natural riparian areas, suggesting that water quality also depends on stream habitat. Moreover, longitudinal variation in water chemistry was proven a simple, useful and low-cost approach to assess the influence of land cover and stream habitat on water quality. Overall results demonstrated that both riparian land use and stream habitat influence water quality and that riparian forests are essential to reduce nutrient export to downstream ecosystems.     

Assessing land use and land cover influence on surface water quality using a parametric weighted distance function

Stream water quality is directly influenced by land use and human practices in the surrounding environment. Understanding such effects and the spatial extent of impacts is essential to generate reliable information for ecosystem-based management of water resources. We identified sources of impact on water quality and characterized indicator-specific landscape influence on samples collected during base flow along the Chubut River (43 °S, 69 °W). We modeled Total Nitrogen (TN), Total Phosphorous (TP), Soluble Reactive Phosphorous (SRP) concentrations and δ¹⁵N of particulate organic matter along the river, as a function of effective contribution areas (A_EC) of Land Use/Land Cover (LULC). A_ECs were calculated by assuming that landscape influence decays exponentially with the Euclidean distance between a given LULC parcel and the sampling point. We calibrated the model to the observations by estimating an indicator-specific decay rate. Agriculture and barren lands were the main sources of phosphate nutrients whereas urban areas were the main source of TN. Radius of landscape influence for SRP (100–180 km) was larger than for TP (10–25 km), reflecting different patterns of mobilization and delivery in the catchment. δ¹⁵N variation was explained by vegetation cover but the influence rapidly decreased (1–4 km) reflecting a mostly autochthonous source of organic matter.     

Impact of coastal land reclamation on ground water level and the sea water interface

Land reclamation in coastal areas may have a significant effect on local ground water systems. Steady-state analytic solutions based on Dupuit and Ghyben-Herzberg assumptions are derived to evaluate this effect. Two situations are considered, both with ground water flow resulting from precipitation recharge: the coastal aquifer of an extensive landmass and an island. The results show that after reclamation, the water table rises and the salt water-fresh water interface moves seaward. The degree of these changes depends on the extent of reclamation and the hydraulic conductivity of the fill material. For the island situation, the reclamation displaces the ground water divide and changes the ground water conditions in the entire island. An unintended advantage of the reclamation is an increase of fresh ground water resource because the reclaimed land can be an additional aquifer and rain recharge takes place over a larger area.     

Effects of land use on water column bacterial activity and enzyme stoichiometry in stream ecosystems

Fifty streams, located in southern Ontario, Canada, were visited in September 2008 to investigate the effect of varying land use, land cover, and associated resource inputs on water column bacterial abundance (BACT), production (BP), and extracellular enzyme activity and stoichiometry. Principle components analysis was used to summarize landscape data, producing three components (PCs), which explained 79.2% of the variability in the data. The PCs grouped into the following gradients: (PC1) urban land use and continuous annual cropping to wetland-like cover, (PC2) rotational cropping to forest-like cover, and (PC3) increasing rural and agricultural land uses with increasing watershed size. These landscape gradients created imbalanced resource availability. Nutrient resources were more abundant in streams with more intensive anthropogenic land uses, but carbon availability was primarily controlled by the abundance of natural land covers (wetland and wooded areas). BACT, BP, and enzyme activities were positively related primarily to nutrient availability and/or anthropogenic land use (Stepwise R ² range: 0.33?C0.73). The ratio of ??-glucosidase to alkaline phosphatase activity approached a 1:1 balance with increasing anthropogenic land use, decreased wetland and forest cover, and increased total dissolved nitrogen. The ratio of leucine-aminopeptidase to alkaline phosphatase activity approached 1:1 with both increased dissolved organic carbon and nitrogen. Moreover, enzyme C:N:P ratios moved closer to 1:1:1 with faster water column bacterial turnover times. These results suggest that water column microbial communities are better able to balance resource availability with growth in streams receiving nutrient subsidies from anthropogenic sources and under these conditions when carbon resources increase.     

极端天气下三峡库区土地利用对河流水质的多时空尺度影响

为探究极端天气下流域内水质对土地利用的响应关系,本研究基于不同空间尺度(1000 m河段缓冲区、500 m河岸带缓冲区及子流域)的土地利用指数以及旱季(2019年11月)、雨季-洪水期(2020年7月)和雨季-干旱期(2022年8月)的水质数据,探究流域内土地利用对水质的多时空尺度影响,从而得到保护流域水质和规划流域内土地利用格局的最佳时空尺度和对水质影响最显著的预测因子。研究表明:(1)流域水质受极端天气影响,降雨会增强水体的稀释能力,高温会加快水中微生物反应速率,具体表现为雨季-洪水期的水质较好,雨季-干旱期次之,旱季较差。(2)土地利用对水质指标的影响存在时空尺度效应,土地利用在子流域和旱季尺度下对河流水质影响最显著。(3)不同土地利用指数对流域水质影响存在差异,耕地、林地、斑块密度、最大斑块指数和边缘密度是影响水质指标最显著的解释变量。其中林地与多数水质指标具有负相关关系,建设用地、耕地、斑块密度与较多水质指标存在正相关关系。本研究结果为合理规划土地利用格局以及保护河流水质提供科学依据,对三峡库区环境可持续发展及生态保护具有一定意义。     

The influence of land use patterns on water quality at multiple spatial scales in a river system

The influence of land use patterns on water quality in a river system is scale‐dependent. In this study, a four‐order hierarchical arrangement method was used to select water sampling sites and to delineate sub‐basins in the Daliao River Basin, China. The 20 sub‐basins were classified into four spatial scales that represented four different stream orders. Pearson correlation analysis was used to quantify relationships between land use composition and the river's physical‐chemical variables for all samples collected. This analysis showed that the presence of forest cover was associated with higher water quality at the scale of the whole basin. The scale effects of land use patterns on water quality were then examined using stepwise multiple regression analysis that compared different land use types with water quality variables. The results from this analysis showed that urban areas, as opposed to forest areas, became the most significant contributors of water pollutants when scale effects were considered. The influence of urban land cover on water pollution was significantly higher at larger scales. The lack of a significant regression correlation for the forest land use type at smaller scales revealed that forest located upstream of the Daliao River Basin did not provide a buffer for improved water quality. Further analysis showed that this result could be because of disproportionate spatial distributions for forest and urban land use types. The topographic characteristics of sub‐basins, such as average slope (S) and size (A), were determined to be secondary explanatory variables that affected land use impacts on stream water quality. Areas with steep slopes were associated with increased water oxygenation, whereas areas with flatter slopes were associated with higher concentrations of pollutants. These results are significant because they can provide a better understanding of the appropriate spatial scale required for effective river basin management in the future. Copyright © 2013 John Wiley & Sons, Ltd.     

Spatial patterning of water quality in Biscayne Bay, Florida as a function of land use and water management

An objective classification analysis was performed on a water quality data set from 25 sites collected monthly during 1994-2003. The water quality parameters measured included: TN, TON, DIN, NH4+, NO3-, NO2-, TP, SRP, TN:TP ratio, TOC, DO, CHL A, turbidity, salinity and temperature. Based on this spatial analysis, Biscayne Bay was divided into five zones having similar water quality characteristics. A robust nutrient gradient, driven mostly by dissolved inorganic nitrogen, from alongshore to offshore in the main Bay, was a large determinant in the spatial clustering. Two of these zones (Alongshore and Inshore) were heavily influenced by freshwater input from four canals which drain the South Dade agricultural area, Black Point Landfill, and sewage treatment plant. The North Bay zone, with high turbidity, phytoplankton biomass, total phosphorus, and low DO, was affected by runoff from five canals, the Munisport Landfill, and the urban landscape. The South Bay zone, an embayment surrounded by mangrove wetlands with little urban development, was high in dissolved organic constituents but low in inorganic nutrients. The Main Bay was the area most influenced by water exchange with the Atlantic Ocean and showed the lowest nutrient concentrations. The water quality in Biscayne Bay is therefore highly dependent of the land use and influence from the watershed.     

Effects of land use on water chemistry in a river draining karst terrain,southwest China

Abstract

The effects of land use on river water chemistry in a typical karst watershed (Wujiang River) of southwest China have been evaluated. Dissolved major ions and Sr isotopic compositions were determined in 11 independent sub-watersheds of the Wujiang River to investigate the spatio-temporal variations in river water chemistry and their relationship to land use. The results show significant spatial variability in pH, major ions, total dissolved solids (TDS), and Sr isotopic compositions throughout the basin. Correlation analysis indicates that nitrogen content is significantly related to forest coverage. Nitrogen and potassium generally have higher values in the rainy season, and the percentage of agricultural land controlled NO₃^- levels, which originate from anthropogenic sources. Forest cover, which varies between 35% and 71%, has no statistically significant impact on river solute concentrations, but the TDS flux is low in sub-watersheds with greater forest cover. Geological sources have a significant influence on pH and Sr isotopic compositions in river water throughout the basin.

Editor D. Koutsoyiannis

Citation Han, G., Li, F., and Tan, Q., 2014. Effects of land use on water chemistry in a river draining karst terrain, southwest China. Hydrological Sciences Journal, 59 (5), 1063–1073.     

Isotopes and sustainability of ground water resources, North China Plain

Ground water in deep confined aquifers is one of the major water resources for agricultural, industrial, and domestic uses in the North China Plain. Detailed information on ground water age and recharge is vital for the proper management of these water resources, and to this end, we used carbon 14 of dissolved inorganic carbon and tritium in water to measure the age and determine the recharge areas of ground water in the North China Plain. These isotopic data suggest that most ground water in the piedmont part of the North China Plain is <40 years old and is recharged locally. In contrast, ground water in the central and littoral portions of the North China Plain is 10,000 to 25,000 years old. The delta18O (deltaD) values of this ground water are 1.7 per thousand (11 per thousand) less than that in the piedmont plain ground water and possibly reflect water recharged during a cooler climate during the last glaciation. The temperature of this recharge, based on delta18O values, ranges from 3.7 degrees C to 8.4 degrees C, compared to 12 degrees C to 13 degrees C of modern recharge water. The isotopic data set combined indicates that ground water in the central and littoral part of the North China Plain is being mined under non-steady state conditions.     

River discharge,land use change,and surface water quality in the Xiangjiang River,China

To compare the impacts of river discharge on the surface water quality of the Xiangjiang River in China, 12 surface water quality parameters recorded at 31 sampling sites from January 1998 to December 2008 along the river and its main tributaries were analyzed. Significantly higher concentrations of total nitrogen, ammoniacal nitrogen, and total phosphorus, and biochemical oxygen demand were observed during low‐flow periods than during high‐flow periods, implying a higher risk to local residents drinking untreated water during low‐flow periods. Pollution indexes, including the inorganic pollution index and integrated pollution index (IPI), were negatively related to impervious surface area (ISA) and cropland area (CLA) when ISA (CLA) was less than 160 (3000) km². However, the relationship was positive when ISA (CLA) was larger than 160 (3000) km², which provided a reasonable explanation for the observed spatial patterns of water quality. Distinct increasing temporal trends for two kinds of pollution indexes were also found. The annual ISA was significantly related to the rapid degradation of water quality from 1998 to 2008, with correlation coefficient (r) values of 0.816 (p = 0.002) and 0.711 (p = 0.014) for the organic pollution index (OPI) and IPI, respectively. However, annual rainfall was negatively correlated with the two indexes with r values of 0.785 (p = 0.002) and 0.448 (p = 0.093) for OPI and IPI, respectively. Our study highlights that decision makers should be more aware of recent increases in the pollution of the Xiangjiang River, especially at downriver sites and during low‐flow periods. Copyright © 2013 John Wiley & Sons, Ltd.     

Delayed impact of new volcanic ejecta on ground water quality

We observed long-term changes in the concentrations of dissolved ions in ground water caused by leachate from new volcanic ejecta deposited on the ground surface of the volcanic Miyakejima Island, Japan. Water samples were collected from nine wells and two rain collectors over a period of more than 10 years, and samples of runoff water were collected periodically. The samples were analyzed for temperature, pH, alkalinity, Cl⁻, and SO₄²⁻; some of the samples were also analyzed for δ¹³C. Because the leachate from the volcanic ejecta contained sulfate, we recorded an increase in SO₄²⁻ concentrations in the (unconfined) well water. The increase in SO₄²⁻ was initially detected between less than 1.4 and 5.2 years after the eruption, showing peak concentrations from 2.4 to 6.4 years after the eruption. This delayed response reflects the transit time of downward-moving SO₄²⁻ in the vadose zone, corresponding to an apparent movement rate of 0.4 to 7.2 cm/d. The rate relates to the mean recharge, represented as a fraction of local mean rainfall, and is calculated using the Cl⁻ balance method. The magnitude of the recorded increases reflects the volume of volcanic mudflow on the ground surface within the basin. For the management of ground water after an eruption, it is therefore important to know the chemical properties of the volcanic ejecta and the spatial distribution of mudflow to estimate the magnitude of the effect of ejecta on ground water quality.