Assessment of Depressional Wetland Degradation, Spatial Distribution, and Geological Aspects in Southern Brazil

Lázaro Zuquette,Moisés Failache,Ademir Barbassa

doi:10.3390/geosciences10080296

Lázaro Zuquette, Moisés Failache + Show 1 more

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https://doi.org/10.3390/geosciences10080296

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Abstract

This paper presents a procedure to study depressional wetlands in southern Brazil and focuses on the mechanisms controlling water dynamics and environmental degradation due to anthropogenic interference. The study is based on an inventory of wetlands, a digital elevation model, the geological and geotechnical characteristics of geological materials, a multitemporal analysis of satellite images, the distribution of land use types, and onsite monitoring of water level and rainfall data. One hundred and twelve depressional wetlands were identified with a total area of 902 ha and a catchment area of 5456.8 ha. These wetlands were grouped into two classes with different hydrological control mechanisms. From the water level monitoring, the wetlands were found to present different hydrological conditions. Before rainy periods, the wetlands were almost dry or had little water; after rainy periods, over half of the wetlands were still dry or had groundwater levels below the surface, and the water levels of the other wetlands increased. The multitemporal analysis showed a reduction in the wetland water surface area from 270 ha in 1991 to 60 ha in 2019, which confirms the monitoring result that the amount of stored water is decreasing because of anthropogenic activities. Anthropogenic activities affect wetland water dynamics because of changes in the landscape and soil characteristics of the catchment area, and drainage of wetland areas by ditches for agricultural water supply; more than 50% of wetlands showed a high degree of change (environmental degradation), with conditions that make restoration or remediation very difficult.

Highlights

Depressional wetlands are characterized as inland aquatic ecosystems that occur in topographic lows with closed or nearly closed elevation contours, which allow surface and groundwater accumulation and typically present weak surface water connections [1] as their surface water levels fluctuate in response to wet and dry periods [2]
We considered different hydrological conditions, which represented the conditions of the water level before and after the rainy season
The wetlands were divided into included different geological materials, relief settings, and characteristics

Summary

Introduction

Depressional wetlands are characterized as inland aquatic ecosystems that occur in topographic lows with closed or nearly closed elevation contours, which allow surface and groundwater accumulation and typically present weak surface water connections [1] as their surface water levels fluctuate in response to wet and dry periods [2] These wetlands are environments with great environmental importance [3,4,5] because they provide habitats for native vegetation and wildlife, reduce erosion during peak events, maintain stream flow during drier periods, recharge aquifers, store precipitation and runoff water, provide atmospheric moisture by evapotranspiration, assimilate and retain pollutants and sediments derived from upland sources, improve water quality, and provide water availability for different purposes such as agriculture and livestock [6]. Moreno-Mateos et al [9] analyzed data from 36 studies of 358 North

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