## 1 Introduction  
Streams draining catchments dominated by agricultural land uses are often exposed to a variety of non-point source contaminants known to degrade water quality and alter key stream ecosystem processes [1]. Agricultural practices can release nutrients and sediments to streams in agricultural areas through use of fertilizers, soil tillage, livestock husbandry and grazing [2; 3; 4]. Nutrients from fertilizers and animal waste (_i.e._, nitrogen and phosphorus) are essential limiting resources for the growth of aquatic vegetation and elevated inputs from agricultural sources have been reported to increase primary productivity in streams [5]. Excess primary productivity may cause periodic hypoxic conditions at night due to plant respiration, as well as from heterotrophic respiration following the die off of plant biomass, stressing ecological communities [6]. However, agricultural practices also have the potential to limit primary production through increased sediment loading and associated reductions in water clarity limiting light penetration to benthic habitats [7]. Growing evidence of the impacts of agriculture on the health of receiving streams and associated downstream ecosystems has made the need to implement effective management strategies to mitigate agricultural effects a major issue in agricultural regions worldwide [8]. In response to the growing recognition of the economic and environmental consequences of nutrient and sediment release from agricultural lands, managerial and structural conservation strategies, or Best Management Practices (BMPs), have been developed to help mitigate the effects of these common stressors. Structural BMPs are designed to reduce loss of pollutants to aquatic ecosystems by enhancing filtration, cementation, and uptake of pollutants in runoff on, or at the edge, of agricultural lands [9]. Common structural BMPs include planting and maintenance of riparian buffer strips, livestock exclusion fences, manure storage facilities, and erosion control structures. Additionally, structural BMPs can be strategically implemented in locations identified as significant contributors of surface water pollutants to help maximize mitigation effects [10; 11; 12; 13]. Many past studies have examined the effectiveness of BMPs in mitigating the impacts of agriculture at small scales and noted improved quality of agricultural runoff [14; 15; 16]. However, past studies exploring the relationship between BMPs and stream ecological condition have shown more equivocal results, despite also frequently reporting reduced concentrations of nutrients and sediments associated with BMP use [14; 15; 17; 18; 19; 20; 21]. To date, past studies have largely focused on taxonomic based measures of community condition, particularly aquatic invertebrates. However, potential for rehabilitation of ecological diversity in agricultural streams may be limited by historical depletion of the regional species pool frequently associated with widespread human activity [22; 23; 24]. As such, ecological benefits associated with BMP use may be most apparent in rehabilitation of ecological processes, such as nutrient dynamics and organic matter input, that are more directly linked to the nutrient and sediment input rates that BMPs are designed to manage [25]. There has, however, been limited examination of the response of river ecosystem processes, such as stream metabolism, to the implementation of BMPs. Stream metabolism is the combination of primary productivity and ecosystem respiration and is thus a measure of the balance between production and consumption of organic matter in a stream. As such, stream metabolism is a critical ecological process providing insight into ecosystem biomass and trophic dynamics [26; 27]. Combined, gross primary productivity (GPP) and ecosystem respiration (ER) can be used to determine the Net Ecosystem Metabolism (NEM; NEM = GPP - ER) and the production to respiration ratio (P/R; P/R = GPP/ER) of the stream.