For over a decade, Salvadorean grassroots movements and non-governmental organisations (NGOs) pursued legal innovations with the aim of protecting their water sources from potentially polluting industrial activities such as mining. They initially drafted bans on mining that would preclude the extractive-based development path embraced by neighbouring countries. Eventually, they scaled up their approach and devised a draft proposal for a transboundary waters treaty that addressed the challenges that the ecological materiality of international watercourses poses to national de jure sovereignty. In so doing, the transboundary watershed has become a useful heuristic, a spatial trope to which Salvadoreans have turned to substantiate their claims to sovereignty over the Lempa River waters that El Salvador shares with pro-mining Guatemala and Honduras – claims imbued with an ethics of care rooted in wartime politics and Catholic morality.

A two-year surface water reconnaissance of the Bogue Phalia and its tributaries was conducted in 1997 and 1998. Cyanazine and metolachlor in surface water samples were quantified using enzyme-linked immunosorbent assays (ELISA). Cyanazine and metolachlor were detected in 101 and 132 of 160 samples, respectively. Cyanazine concentrations ranged from 0.1 to 2.2 g L−1 and exceeded the U.S. Environmental Protection Agency (EPA) lifetime health advisory level (HAL) of 1 g L−1 in eight samples. However, concentrations never exceeded the HAL for shorter exposure times. Metolachlor concentrations never reached the lifetime HAL of 100 g L−1. Metolachlor concentrations ranged from 0.1 to 20.6 g L−1. Metolachlor was detected more frequently and found to be more persistent throughout the growing season than was cyanazine. Higher cyanazine and metolachlor concentrations were detected at sampling dates that coincided with herbicide applications. One of the Bogue Phalia's tributaries, Clear Creek, was found to be a point-source of cyanazine for the watershed.

This study evaluates first- and second-best trading policies for regulating watershed phosphorus under asymmetric information. The trading policies are differentiated on the degree to which regulators observe point and nonpoint source abatement efforts. The efficiency losses attributable to these informational asymmetries and those of the second-best policies can be measured in social welfare, and provide regulators the shadow value of foregoing first-best measures. Given representative monitoring costs from national water monitoring programs, it is shown that under asymmetric information, the chosen second-best trading policies outperform first-best policies by 11% in the control of watershed nutrient pollution.

The optimal size and location of an invasive species population depend upon spatially differentiated biological growth, economic costs, and damages. Although largely absent from most economic models, spatial considerations matter because the likelihood and magnitude of the invasion vary spatially and the threatened assets may be unevenly distributed across space. We map the current and future populations of an invasive species, Miconia calvescens, on Oahu, Hawaii, and the potential damages to water quantity, quality, and endangered-species habitat, and weigh these against treatment costs. We find that optimal densities vary from approximately 1% to 18% cover throughout the island.

Agriculture in general and intensive animal production in particular can degrade the environment, especially as a consequence of the overuse of nutrients. Intensively grazed dairy systems, defined by the presence of foraging animals in the landscape, are often considered a more benign approach to dairy production with perceived smaller impacts due to the reduced requirement for manure disposal. However, grazing dairy cows contribute nutrients and pathogens in excreta, and sediment through landscape deformation. These impacts can dramatically increase in parts of the farm such as feeding, watering and sacrifice areas, laneways and night paddocks where animals are concentrated and spend a disproportionate amount of time. Other practices such as the disposal of dairy shed or dairy factory effluent and cultivation of fodder crops can also pollute the environment. A common approach to reduce nutrient, pathogen and sediment losses from dairy farms is to establish buffer zones in riparian areas that act as an interface between upland land use and waterways. This is generally done by fencing riparian areas to exclude stock and revegetating with understory and overstory species, with the aim of increasing infiltration, trapping sediment and decreasing contaminant losses from upland pastures. However, poorly designed and managed riparian areas may themselves contribute to further environmental degradation. Rarely is an integrated approach, including factors such as animal behavior and dairy farm management practices, as well as an analysis of landscape and riparian hydrology used in developing riparian management recommendations for individual farms. This paper reviews the threats posed by intensively grazed dairy systems, approaches to improve riparian zone management and recommends future research needs.

Radar rainfall nowcasting at short lead times has important hydrometeorological applications in the fields of weather prediction and flood forecasting. The predictability of rainfall events can vary significantly with scale as smaller storm features are less predictable than the storm envelope motion. As a result, various techniques have been developed for filtering a radar image and deriving short-term forecasts from the more predictable, larger storm scales. In this study, the effects of image filtering on radar nowcasting performance using the Storm Tracker Nowcasting Model (STNM) are evaluated. Radar rainfall nowcasts are evaluated for three storms exhibiting varying degrees of organisation over the Arkansas-Red River basin. In each case, it is found that the nowcast skill decreases with the forecast lead time, increases with the verification area used around a forecast location, and decreases with higher rainfall thresholds. Furthermore, it is demonstrated that a set of properly tuned filtering nowcasts are superior to simple ‘persistence’ and slightly better than ‘uniform advection’. At the scale of a large hydrologic basin (∼ 6000 km2), filter-based nowcasting is shown to capture the temporal variation in rainfall amount and its spatial distribution based on a set of catchment-based metrics. Finally, a method for relating changes in nowcasting skill to errors associated with storm dynamics not captured by image filtering techniques is evaluated.

The amount and annual net accumulation of above-ground dead woody material were quantified in a tropical deciduous forest in western Mexico. Three plots were located within a small watershed (16 ha) and distributed along a 150-m-elevation gradient (Upper, Middle and Lower plot). Total amount of above-ground dead phytomass (fine + coarse) was 27.2 Mg ha-1. Coarse dead category (branches + logs) made up 70.6% (19.2 Mg ha-1) of the total. The rest comprised the fine fraction, which was lying on the forest floor as surface litter. Of the total coarse dead woody mass, 70.8% was standing, hanging or still attached to live trees (13.6 Mg ha-1). Dead wood net accumulation was 6.6 Mg ha-1 y-1; 58% of this was coarse woody material and the rest comprised the fine litterfall fraction. The amount of standing, hanging/attached dead branches (2-20 cm circumference) varied significantly among plots, with the highest value in the Upper plot. Dead wood net accumulation was similar between the Upper and Middle plots, and significantly higher than the Lower plot. Compared to the intact canopy, the removal of dead mass (hanging/attached dead branches and standing dead logs) caused a significant decrease in throughfall nutrient concentration and nutrient flux by this pathway.

Today there is much concern about the potential contamination, overuse and development of scenic rivers in more or less pristine environments. The objective of this work was to quantify the spatial and temporal changes in land-use occurring in a watershed draining a nationally protected river. The Buffalo National River of Arkansas was chosen to serve as an example of how Geographic Information System (GIS) technology can rapidly assess the environmental changes that have occurred within a watershed. GIS was used to develop a spatial database of the watershed and to describe differences in land-use data from five sample years during 1965–92. Over this time span, approximately 40 000 ha of forest were lost and converted primarily to pasture. The average rate of loss of forest was 1480 ha/yr. During this same period, the average rate of gain of pasture was 1381 ha/yr. Buffer analyses showed that pasture increased at a higher percentage rate in the buffer zones surrounding the Buffalo River than in the tributaries of the Buffalo River, and a large proportion of the increase was on higher slopes. Land-use changes were dynamic with a greater area converted to pasture than area of pasture converted to forest in the watershed. The cleared forest lands were mostly near older pastures and along streams. The reforested lands tended to occur in the more isolated areas. The Buffalo River Watershed has undergone changes in land-use that may have had impact on the water quality of the region.

Soil and water conservation and improved crop management programs were initiated in 1983 to increase the productivity of a dryland vertisol watershed in the state of Andhra Pradesh in the semi-arid tropical region of India. This was one of 47 model watersheds developed by the Government of India. The integrated program consisted of measures to conserve soil and water, such as a percolation tank, grading, checks, and deep tillage, on which were superimposed improved crop management practices (e.g., cultivars, fertilizers, and timeliness in operations), carried out with the farmers' cooperation and partial payment. All participants were surveyed in 1983, before starting the program, and 1988, after completing the program. The equilibrium water levels in open wells increased about 50 cm, which allowed sugarcane to be introduced. About 10% additional area was reclaimed and cultivated after construction of a diversion dam. Fodder supply improved because of the growth of natural grasses on terraces formed by stone checks in waterways. Soil and water conservation efforts reduced runoff about 26%. Ground cover increased by 38% because of increased cropping intensity, and income per capita grew by 67% per year. Thus, the integrated approach conserved natural resources and improved productivity.