Contextualizing waterscape health in a subtropical rangeland
Date
2021-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Freshwater ecosystems are threatened globally by environmentally impactful agriculture. An ever-
increasing population drives intensive agricultural production, putting immense
pressure on freshwater ecosystem integrity. It is recognized that agriculture needs to be more
environmentally sustainable. One way to achieve this is for agricultural production to align with,
and support, local ecosystem functions while remaining within the other conventions
(economic and social) of sustainable development. Livestock grazing areas (rangelands) are a
major component of the total agricultural land use surface in Southern Africa. Within these
rangelands, perennially inundated waterbodies across the landscape (waterscape) occur in a
variety of hydrogeomorphic formats, both natural and artificial (depressions, deposition
pools, weirs and dams) and are here referred to individually as waterbodies. Thus, the
broad aim of this study is to gain some insight into the biotic and abiotic characteristics of
waterscape health in rangelands of the Eastern Coastal Belt Ecoregion
(ECBE).
Artificial waterbodies, like excavated depressions, constructed dams and weirs are common features
in rural South African rangelands. Often, these excavated or constructed waterbodies
completely modify characteristics of those that occur naturally, impacting waterscape
ecosystem functions. However, artificial waterbodies can also be complementary to naturally
occurring waterbodies in degraded waterscapes, improving overall waterscape biodiversity and
resilience. In chapter 2, I compare environmental variables and dragonfly assemblage
composition of natural and artificial waterbodies to demonstrate that intact, high order,
naturally occurring forested stream deposition pools are an irreplaceable habitat for
threatened aquatic biodiversity in the ECBE, vulnerable to impoundment and channel
modification. I also show that well-managed excavated depressions provide valuable habitats
for lentic biota in the region. I suggest agro-conservation strategies that aim to reduce
disturbance frequency and channel modification in and around high order stream channels. Farm
managers should promote artificial depressions outside of stream channels as a primary source of
livestock drinking water.
Determining significant environmental and biological characteristics of healthy and compromised
agro-ecological systems is vital to regional conservation planning and restoration. In chapter 3, I
use the Dragonfly Biotic Index (DBI) to determine which biotic and abiotic variables drive
waterbody health in the ECBE. I also illustrate the composition assemblage of dragonflies
responsible for high
and low DBI/ site scores. Again, I highlight the importance of reducing intensity and frequency of
livestock disturbance in stream deposition pools. I recommend considering individual waterbody habitat heterogeneity as a key feature in maintaining waterbody integrity. Invasive tree clearing and facilitating a compositionally and structurally diverse woody riparian component, appropriate for its hydrogeomorphic type is fundamental to regenerating ecosystem functions.
A transition towards sustainable livestock production means departing from resource intensive livestock systems. To achieve this, we need to identify appropriate scenarios for agroecology and contextualize agro-ecosystem. In the coastal plains of the ECBE, large savanna and azonal grasslands are suitable for well-managed ruminant livestock grazing, where ruminants play a vital role in maintaining ecosystem services. Here, analyzing local hydrogeomorphic features and biological attractors provides tangible methods to improve biodiversity conservation and perennial surface water resilience within a waterscape. This study also highlights that individual waterbody habitat heterogeneity is inimitable for biodiversity conservation at a global scale. I urge rangeland managers to consider and mimic all features of naturally occurring individual waterbodies within a waterscape for successful integration of rangelands and freshwater conservation. In the ECBE, extensive ruminant livestock keepers should increase frequency of depressions as a primary source of drinking water to reduce disturbance at streams.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MScConsEcol)--Stellenbosch University, 2021.
Keywords
Agroecology -- South Africa-- Eastern Coastal Belt Ecoregion, Ecosystem management, Freshwater, Rangelands -- Water-supply -- South Africa -- Eastern Coastal Belt Ecoregion, Agriculture -- Environmental aspects, Water quality management, UCTD