Spatial Relationships Between Water Quality and Pesticide Application Rates in Agricultural Watersheds

Abstract

Pesticide applications to agricultural lands in California, USA, are reported to a central data base, while data on water and sediment quality are collected by a number of monitoring programs. Data from both sources are geo-referenced, allowing spatial analysis of relationships between pesticide application rates and the chemical and biological condition of water bodies. This study collected data from 12 watersheds, selected to represent a range of pesticide usage. Water quality parameters were measured during six surveys of stream sites receiving runoff from the selected watershed areas. This study had three objectives: to evaluate the usefulness of pesticide application data in selecting regional monitoring sites, to provide information for generating and testing hypotheses about pesticide fate and effects, and to determine whether in-stream nitrate concentration was a useful surrogate indicator for regional monitoring of toxic substances. Significant correlations were observed between pesticide application rates and in-stream pesticide concentrations (p < 0.05) and toxicity (p < 0.10). In-stream nitrate concentrations were not significantly correlated with either the amount of pesticides applied, in-stream pesticide concentrations, or in-stream toxicity (all p > 0.30). Neither total watershed area nor the area in which pesticide usage was reported correlated significantly with the amount of pesticides applied, in-stream pesticide concentrations, or in-stream toxicity (all p > 0.14). In-stream pesticide concentrations and effects were more closely related to the intensity of pesticide use than to the area under cultivation.

Influence of Watershed Scale Atrazine Reduction Practices on Pesticides and Fishes within Channelized Agricultural Headwater Streams

“…We were not able to obtain information on the exact locations of atrazine reduction practices and other conservation practices within our study sites because this information is not available for privately-owned lands due to federal privacy regulations and bureaucracy. Increasing proximity of insecticide application to sampling sites resulted in increased insecticide concentrations within a California stream (Hunt et al, 2006). Additionally, small-scale hydrological characteristics within a watershed can create hotspots capable of facilitating the transport of pesticides into adjacent streams (Freitas et al, 2008).…”

“…Water samples for pesticide measurements and fishes were collected in the spring and summer from a treatment stream (watershed size -3.89 km 2 ) that received atrazine reduction practices within 26 to 31% of its watershed during the first two years and then the watershed usage of these practices was reduced to less than 6% in the last four years. We also collected water samples and fishes during the same time from a control stream (watershed size 4.54 km ticide concentrations often lead to death of stream organisms and subsequently alter stream population and community characteristics (Hunt et al, 2006). Even low levels of pesticide concentrations may lead to sublethal effects involving changes to physiology, morphology, and behavior of individual stream organisms (Crawford, 2001;Dabrowski et al, 2002;Maltby and Hills, 2008).…”

“…The ecological benefits of reducing pesticide concentrations are also relatively unknown because most previous watershed scale assessments have not evaluated ecological responses (Table 1). Laboratory bioassays conducted to determine the toxicity of the water collected from a California stream found that increasing pesticide concentrations and increasing the proximity of pesticide applications to the sampling sites was correlated with increasing invertebrate mortality (Hunt et al, 2006). There is a critical need to determine if pesticide reduction practices lead to reduced impacts on aquatic life in streams.…”

Problems with determining the particle size distribution of chalk soil and some of their implications

“…When these fractions have been determined in the laboratory by sieving, sedimentation or laser methods, they are referred to as the particle size distribution (psd) of the soil. Published studies (Hunt et al, 2006;Lewis et al 2003; http://www.cdms.net/ldat/ld6NS001.pdf) and DEFRA's RB209 'Fertiliser Recommendations for Agricultural and Horticultural Crops' (MAFF, 2000) indicate that psd should be taken into account in determining rates of fertilizer and pesticide application to the soil. Inaccurate determination of soil psd where soil has developed on chalk in England has clear implications for decisions in agricultural management, particularly in relation to the leaching of nitrate.…”

Hydrogeochemistry and brine evolution of Maharlou Saline Lake, southwest of Iran

“…Hunt et al 2006). The accuracy of the multi probe device was also checked by the Geological survey of Iran Hydrochemistry team in Chabahar bay and Oman Sea, comparing the obtained results with the availabe CTO…”