Nitrogen, phosphorus and silicon in riparian ecosystems along the Berg River (South Africa): The effect of increasing human land use

Abstract

The Berg River is one of the main rivers in the Cape Region; it is essential for the local economy and ecology, as it supplies water to agriculture and industries, provides drinking water for the greater Cape Town region, and supports rich aquatic ecosystems. The Berg River is impacted by both diffuse pollution from agricultural run-off and point-source pollution from urban and industrial wastewater. Construction of a dam on the headwaters of the Berg River in 2007 has changed the hydrology of the upper catchment. Pelagic nutrient dynamics in the Berg River are well documented. The opposite is however true for riparian nutrient dynamics. We studied changes in riparian nutrient storage over a gradient in elevation (a proxy for flooding frequency and drought) and human influence (the Berg River dam and lateral nutrient and pollutant input). Our results show that nutrient concentrations in the riparian sediments reflect nutrient concentrations in the river. N concentrations in the sediment increased up to 1 000%, while P concentrations rose up to 200% with increasing human influence. For biogenic Si, we found generally low concentrations throughout the whole gradient sampled (all < 0.5 mg BSi g -1 sediment). Sediments closer to the river appear to have more efficient recycling and export of nutrients into the river. Overall, we conclude that the observed patterns indicate the necessity of incorporating nutrient status and management of riparian habitats in the Berg River monitoring strategy.

Dissolved phosphorus transport from soil to surface water in catchments with different land use

“…Sharpley et al 2000 ; Cordell et al 2009 ). Struyf et al ( 2012 ) found a twofold increase in P concentration in the sediment of the Berg River, South Africa, under increasing human influence. Phosphorus is a non-renewable resource and therefore P losses are detrimental to the long-term sustainability of agriculture.…”

Urbanisation, climate change and its impact on water quality and economic risks in a water scarce and rapidly urbanising catchment: case study of the Berg River Catchment

“…In light of De Villiers 2007, it is of concern to note the findings of Struyf et al (2012), who investigated the changes in riparian nutrient dynamics along the Berg River. They found that nutrient concentrations in the sediments within the riparian zone reflect the concentrations of nutrient in the Berg River.…”

“…Struyf et al (2012) highlighted that their study indicated that if the changes in the hydrological cycle, in particular reduced flow, and water quality levels suggested in De Villiers (2007) were to come to fruition, it would be highly likely that a number of ecosystem goods and services would be impactedincluding the natural filter function of the river system. Furthermore, Struyf et al (2012) suggest that due to the impact of the high nutrient levels on the riparian zone, it may in future become a source of nutrients for the river, further compounding the challenges in managing the river. Paulse et al (2007) utilised a section of the Berg River to compare different enumeration techniques for the investigation of bacterial pollution.…”

“…The water quality in the Berg River Catchment has been monitored since, at least, 1967(De Villiers 2007. Since 2005 there have been a number of studies (Görgens & de Clercq 2005;Clark & Ractliffe 2007;Jackson et al 2007;Paulse et al 2007;Struyf et al 2012) that have considered different aspects of water quality in the Berg River and other rivers in the region (Cullis et al 2018). These studies have utilised data sets dating back as far as 1985.…”

Invasion of a Widespread, Non‐Native Grass Causes Downstream Reductions in Bioavailable Silica

“…Such gaps in knowledge lead to our inability to model silica dynamics on regional or continental scales, as demonstrated by Lauerwald et al (2013). One reason that floodplain and riparian processes are poorly understood is that, although we know many plants create siliceous phytoliths in their biomass (e.g., Conley 2003; Cary et al 2005; Struyf et al 2012), we know little about how and whether those phytoliths accumulate in the oft‐saturated soils of riparian zones. Another challenge in quantifying riverine silica sequestration is that riverine sediments are notoriously difficult to date because riverine sedimentation is spatially and temporally discontinuous.…”