Native forest cover safeguards stream water quality under a changing climate

Abstract

Ensuring a sufficient and adequate supply of water for humans and ecosystems is a pressing environmental challenge. The expansion of agricultural and urban lands has jeopardized watershed ecosystem services and a changing climate poses additional risks for regional water supply. We used stream water quality data collected between 2000 and 2014, coupled with detailed precipitation and land cover information, to investigate the effects of landscape composition and short‐term precipitation variability on the quality of water resources in the state of São Paulo, Brazil. The state is home to over 45 million people and has a long history of human landscape modification. A severe drought in 2014–2015 led to a major water crisis and highlighted the fragility of the regional water supply system. We found that human‐dominated watersheds had lower overall water quality when compared to forested watersheds, with urban cover showing the most detrimental impacts on water quality. Forest cover was associated with a better overall water quality across the studied watersheds, with forested watersheds having low turbidity and high dissolved oxygen. High precipitation led to increased turbidity and fecal coliforms levels and lower dissolved oxygen in streams but these effects depended on watershed land cover. High precipitation diluted concentrations of nitrogen and dissolved solids in highly urbanized watersheds but exacerbated turbidity in pasture‐dominated watersheds. Given the high costs of water treatment in densely populated regions, there is a pressing need to plan and manage landscapes in order to ensure adequate water resources. In tropical regions, maintaining or restoring native vegetation cover is a promising intervention to sustain adequate water quality.

Dispersed Urban‐Stormwater Control Improved Stream Water Quality in a Catchment‐Scale Experiment

“…SCMs are therefore most likely an appropriate tool for addressing this legacy problem for a long-term achievement of the EC target. Such legacy effects, and indeed contemporary impacts such as inadequate sewage treatment and disposal (Piffer et al 2021), are likely to be common in many urban catchments globally. Where problems such as inadequately treated sewage or industrial effluent are present, they should clearly be management priorities.…”

“…Regionally, the impacts of urban land use on river water quality can be disproportionately large (e.g. Piffer et al 2021). However, alternative land and water management practices have the potential to protect downstream waters and provide many cobenefits to the world's cities, including greater water supply security (Walsh et al 2016).…”

“…Streams of urban catchments are typified by flashy flow regimes, incised and deepened channels and compromised water quality leading to shifts in their ecological structure and function (Walsh, Roy, et al., 2005). Regionally, the impacts of urban land use on river water quality can be disproportionately large (e.g., Piffer et al., 2021). However, alternative land and water management practices have the potential to protect downstream waters and provide many co‐benefits to the world's cities, including greater water supply security (Walsh et al., 2016).…”

How does land use cover change affect hydrological response in the Atlantic Forest? Implications for ecological restoration

“…The region is subject to a negative tradeoff that represents a faster increase in evapotranspiration due to increased leaf cover and a gradual improvement in soil water infiltration conditions (Ferraz et al, 2020). In these regions, the recommendation is to identify critical regions in relation to water availability considering climatic conditions (Ponce et al, 2000) and local conditions (of Assis et al, 2011) and, in these areas, give focus more on the restoration of riparian strips aiming at water quality (Souza et al, 2013;Piffer et al, 2021) and adoption of techniques that allow better evolution of soil structure and lower evapotranspiration rates such as agroforestry systems (Murta et al, 2021).…”

Uso do solo e regimes de precipitação como determinantes para a qualidade da água

“…Estes benefícios provenientes dos ecossistemas são conhecidos como "Serviços ecossistêmicos" (SE) (Millennium Ecosystem Assessment, 2005), dentre os quais podemos destacar a provisão de água, incluindo tanto qualidade quanto quantidade de água (Piffer et al, 2021). A utilização do termo "qualidade da água" refere-se às características físicas, químicas e biológicas de um corpo d'água (Wang, 2001) e pode variar de acordo com o local, o clima e a presença de diferentes contaminantes (Likens & Buso, 2006;McKee et al, 2001;Ometo et al, 2000).…”