Cross‐ecosystem impacts of stream pollution reduce resource and contaminant flux to riparian food webs

Abstract

The effects of aquatic contaminants are propagated across ecosystem boundaries by aquatic insects that export resources and contaminants to terrestrial food webs; however, the mechanisms driving these effects are poorly understood. We examined how emergence, contaminant concentration, and total contaminant flux by adult aquatic insects changed over a gradient of bioavailable metals in streams and how these changes affected riparian web-building spiders. Insect emergence decreased 97% over the metal gradient, whereas metal concentrations in adult insects changed relatively little. As a result, total metal exported by insects (flux) was lowest at the most contaminated streams, declining 96% among sites. Spiders were affected by the decrease in prey biomass, but not by metal exposure or metal flux to land in aquatic prey. Aquatic insects are increasingly thought to increase exposure of terrestrial consumers to aquatic contaminants, but stream metals reduce contaminant flux to riparian consumers by strongly impacting the resource linkage. Our results demonstrate the importance of understanding the contaminant-specific effects of aquatic pollutants on adult insect emergence and contaminant accumulation in adults to predict impacts on terrestrial food webs.

Importance of Riparian Zone: Effects of Resource Availability at Land-water Interface

“…Thus, visitation rates of pollinators normally preyed upon by adult dragonflies increased, and therefore increased plant reproduction in the adjacent riparian habitats [114]. Such cross-ecosystem connectivity is crucial to assess anthropogenic effects of landscape disturbance on metaecosystem dynamics [115][116][117].…”

“…Not all cross-system subsidies are beneficial to recipient ecosystems, as subsidies can also propagate pollutants [116,117,152] and pathogen [178] to consumers, and lower ecosystem stability [179]. Contaminants in aquatic ecosystems such as heavy metals and polychlorinated biphenyls (PCBs) can be accumulated in terrestrial predators through directly feed on emerging aquatic insects.…”

Handling Water through Irrigation Watershed Management for Coping with Stream Pollution Dilution in Phetchaburi River, Thailand

“…It is remarkable for careful observation when flow velocity increased up to 377 m 3 /s that trends of BOD and DO looked the same downslope due to much more rainwater of heavy rainstorm is usually plenty of DO and also increasing BOD in stream water. For this reason, the decrease of DO because it was used for bacterial organic digestion process that made BOD lowering as well but interesting point was on the city zone in terms of urban rainwater in city zone being composed of DO while drastic increases of BOD was occurred by erosion process due to much more excessive rainwater on the ground surface with very less infiltration rate (Cazelles et al, 1991;Loomis et al, 2000;Burnett et al, 2007;Chen et al, 2008;Liu et al, 2009;Chu et al, 2010;LERD, 2012;Mangimbulude et al, 2012;Rakthai, 2012;Kraus et al, 2014).…”

“…In reference to aforesaid issues, watershed management, which is defined as the environmental systems for managing water, has been initiated in order to relieve stream water quality problems down to at least to meet the desirable quality water for specific targets (Chunkao et al, 1981;Chu et al, 2010;Chunkao et al, 2010). In other words, there are some watersheds that specify its own management criteria for specific water yields (quantity, quality, and flow regime) but it is usually under the multiple use purposiveness for general public land areas as explained by Robinson and Maris (1985); Linsley et al (1988); Cazelles et al (1991); Tanji et al (2006); However, Chunkao (2008); Valipour et al (2009) ;Wang et al (2010); Mangimbulude et al (2012) and Kraus et al (2014) described that the specific purpose in watershed management would be provided to serve needs of water managers in order to achieve the project goal without any delay of work program.…”

“…(Chunkao et al, 1981;Chunkao, 2008). The key points on irrigation watershed management is to handle water yields in stream for maintaining optimum quantity, quality, and flow regime in order to ready-use for irrigating, self purifying, and aquatic animal and plant ecology in wet and dry seasons without lacking the desirable quality water flow (Chunkao, 1981;Liu et al 2009;Kraus et al, 2014). Unluckily, most of rivers in the whole country has been changed the forested cover in headwater to become the cultivated and human settlement areas that causing the streams running dry in summer but high amount of excess water in wet season and turning to be flooded on flatlands as pointed out by Wang et al (1978); Chunkao et al (1981); Vagnetti et al (2003); Burnet et al (2007); Chunkao et al (2008); Liu and Chen (2009) ;Wahla et al (2008); Chu et al (2010); PCD (2010); Chunkao et al (2012); PCD (2013).…”