Evaluating land use impacts on water quality: perspectives for watershed management

Abstract

Human activities threaten the integrity of watersheds. We aimed to investigate the impact of land use on water quality, adopting a multiscale approach. We collected water samples from twelve streams in Southern Brazil and conducted limnological analyses (physical, chemical, and biological) during the dry season. We used the water quality index based on the quality standards of Canada and Brazil. Land use percentage was measured in two groups (local scale and network scale). Environmental variables were summarized through Principal Component Analysis, and we organized them into Linear Models, integrating the percentage of land use classes and terrain slope in the Multifit formula. Statistical analyses were performed using the R software. Results indicated contamination by lead, chromium, copper, nitrogen, and Escherichia coli in water samples. The Canadian Water Quality Guidelines for the Protection of Aquatic Life resulted in an index ranging from 23.3 to 47.3, compared to the Brazilian Resolution No. 357/2005 for Class 2, which had an index ranging from 47.5 to 100. This disparity is attributed to the more rigorous and sensitive monitoring approach adopted by the Canadian guidelines. Riparian forests which are up to 50 m wide are associated with improved water quality. Agricultural and urban activities were the main contributors to water quality degradation in an area extending up to 1000 m from the watershed. We emphasize the importance of a multiscale approach in watershed management and public policies, considering not only riparian forest preservation, but also human activities throughout the watershed. It is crucial to prioritize science-based environmental public policies and strengthen enforcement to prevent increasingly pronounced environmental collapses. We have identified the urgency to reformulate CONAMA Resolution No. 357/2005 with a more conservationist and ecosystem-oriented approach, as well as to propose modifications to the Brazilian Forest Code, particularly regarding the buffer zones of permanent preservation areas. Thus, this study can provide insights, such as incorporating the “effect scale,” to enhance water resource management in landscapes heavily influenced by human action, contributing to the advancement of future research in freshwater ecosystems.

Estimating Thresholds of Natural Vegetation for the Protection of Water Quality in South African Catchments

“…It would be inappropriate, for instance, to focus on managing land use at one spatial scale (e.g., within riparian areas) while ignoring land use at other scales (e.g., across whole catchments) (Lorion & Kennedy, 2009;Iñiguez-Armijos et al, 2014;Cole et al, 2020;Nobre et al, 2020). The multi-scale management perspective advocated by other studies is thus endorsed, and the necessity of determining and applying thresholds at both riparian and whole-catchment scales is likewise confirmed (Strayer et al, 2003;Schiff & Benoit, 2007;Zhou et al, 2012;Ding et al, 2016;de Mello et al, 2018;Park & Lee, 2020;Song et al, 2021;Pei et al, 2023;Siqueira et al, 2023).…”

“…To this end, decades of research and literally hundreds of independent studies have demonstrated that relatively simple statistical models can be effective tools that support informed decision-making when developing integrated management plans (du Plessis et al, 2015;Giri & Qiu, 2016;Rodríguez-Romero et al, 2018;Ullah et al, 2018;Lacher et al, 2019;Cheng et al, 2022;Li et al, 2022a;Gobry et al, 2023). These studies show that while the relationship between LULC and water quality is undeniably complex and often regionally specific, certain anthropogenic classes of LULC (e.g., built-up areas, farmland, mines, and forestry plantations) tend to be sources of diffuse pollution, whereas most classes of natural vegetation (e.g., indigenous forests, grasslands, and wetlands) serve as sinks by intercepting, filtering, and remediating contaminated runoff (Lintern et al, 2018;Fernandes et al, 2021;Wang et al, 2021;Cheng et al, 2022;de Mello et al, 2022;Li et al, 2022b;Caldwell et al, 2023;Qiu et al, 2023;Siqueira et al, 2023;Xu et al, 2023a;Zhang et al, 2023).…”

Evaluating the Environmental Quality of Forest Remnants Using Landscape Metrics

“…The high potential of the Atibaia and Jaguari basins for water production makes them more sensitive to the process of urbanisation, densification and poor land management, which can affect water availability and cause losses in the quantity and quality of water [85]. On the other hand, the study carried out by Siqueira et al [86] in Southern Brazil showed that the areas characterized by agricultural and urban activities negatively affect the quality, while the presence of riparian forests within a radius of 50 m improve water quality. Garcia et al [87] also showed that springs located within an area of environmental preservation and with minimal anthropogenic intervention (e.g., Mata de Santa Genebra, a forest remnant located in the Anhumas river basin) had higher water quality than springs located in areas of strong anthropogenic intervention or without riparian forest in their surroundings.…”

Estimating thresholds of natural vegetation for the protection of water quality in South African catchments

“…Paradoxically, the same anthropogenic activities that are dependent upon a reliable supply of clean water are often responsible for its degradation. While the relationship between land use/land cover (LULC) and water quality is undeniably complex and often regionally-specific, decades of research have confirmed that urban areas, agricultural land, mining operations, and commercial forestry plantations all tend to be sources of diffuse pollution, whereas natural vegetation serves as a sink by intercepting, filtering, and remediating contaminated runoff (Lintern et al, 2018;Kajitvichyanukul & D'Arcy, 2022;Siqueira et al, 2023). However, while the importance of an integrated catchment management approach is often affirmed in principle, and notwithstanding the wealth of published research that supports this perspective, there is arguably a need for further work that provides stakeholders and policymakers with the knowledge necessary to ensure that land and water resources are managed in a coordinated fashion (Gooch & Stålnacke, 2010;Falkenmark et al, 2016;Locke, 2024b).…”