Nyl River Research Articles

Determination of sediment quality in the Nyl River system, Limpopo Province, South Africa

The importance of wetland management and conservation is becoming more and more prevalent in the world today. It is thus important to determine baseline contamination values for wetlands to assist in making informed management decisions. Sediment from the Nyl River flood plain in the dry Limpopo Province was analysed using sequential extraction and ICP-MS to determine baseline metal concentrations, and bioavailability thereof. Eight heavy metal (Cu, Cd, Cr, Al, As, Zn, Mn, Pb) concentrations were determined and compared to sediment quality guideline values to assess sediment quality. Fractionation of the elements was also noted to assess the bioavailability of the metals. The results indicated that the sediment is of a fair quality in comparison to the sediment quality guideline values. They also indicate that the metals will only become available in the presence off strong reducing agents as most off the metal concentrations were recorded in the 4th and 5th fractions obtained from the Tessier sequential extraction of the sediment samples. The study concluded that the sediment is of a fair quality and that it poses little potential threat to the system.

High-resolution shallow reflection seismic integrated with other geophysical methods for hydrogeological prospecting in the Nylsvley Nature Reserve, South Africa

Two perpendicular high-resolution shallow seismic and resistivity profiles were acquired to assist in imaging the near-subsurface sedimentary architecture for hydrogeological prospecting in the Nylsvley Nature Reserve along the Nyl River floodplain in South Africa. We deployed 48 channels of 14 Hz geophones with 1–2 m dense source-receiver spacing providing fold coverage of 24 (line 2) and 48 (line 1). The resistivity profiles were acquired with a Schlumberger electrode configuration with 2–3 m electrode spacing and a total of 40 steel electrodes. The raw seismic shot records were characterized by low-frequency, high-amplitude source-generated noise (surface and guided waves). Reflections from bedrock were not obvious. To enhance the reflected seismic signal, we employed an extensive seismic processing workflow which enhanced the seismic reflectivity on the stacked sections. The seismic reflection interpretation was constrained and integrated with seismic refraction and resistivity tomography, and the one-dimensional multichannel analysis of surface waves to generate the model that best represents the real subsurface geological model. The integrated results show the bedrock-overburden contact at 8–12 m depth, which correlates well with boreholes drilled in the area. In addition, the reflection seismic and refraction tomography show the bedrock undulation and velocity changes associated with erosional surfaces or weathered/fracture systems. We further interpret these characteristics to be associated with groundwater movement and storage related to the fractured/weathered zone within the bedrock. The integrated data also delineate the interface between the unsaturated sand and saturated sand-gravel that represents the groundwater water table. This study demonstrates the potential of combining several surface geophysical techniques for near-surface investigations, especially for hydrogeological prospecting.

A multivariate examination of 'artificial mussels' in conjunction with spot water tests in freshwater ecosystems.

Metal pollution in aquatic systems is considered a serious environmental issue globally due to their ability to accumulate in aquatic environments. Wetlands are vulnerable to this pollution as they are known to trap toxins, removing them from the water. Artificial mussel technology, originally developed for marine environments, was applied to this freshwater system and spot water samples were collected. The Nyl River floodplain (Ramsar classified) is one of the largest and most ecologically significant wetlands in South Africa. The aims of this study were to determine metal contamination along the Nyl River system by means of artificial mussels (AM) and water ICP-MS analysis and to determine whether the use of AMs in conjunction with spot water testing could give more insight into the pollution in freshwater wetlands. The concentrations of Al, Cd, Cr, Co, Cu, Fe, Mn, Ni, Pb and Zn were determined at seven sites. It was determined that the levels accumulated by the AMs differed in spatial and temporal trends when compared to spot water samples. It was determined that there were high levels of some metals found in the spot water tests that were not corroborated by the AMs results, which could indicate isolated pollution events. The use of AMs in conjunction with spot water testing was determined to be beneficial in gaining deeper insight into water metal conditions in dynamic freshwater systems.

Use of diatom indices to categorise impacts on and recovery of a floodplain system in South Africa

The trophic status of the Ramsar-accredited Nyl River floodplain, which is stressed by sewage treatment effluents, and its ability to restore normal conditions, were assessed in 2014–2015 using diatoms as biological indicators. The Trophic Diatom Index, Specific Pollution Sensitivity Index and the Generic Diatom Index were used to characterise water quality under high and low flow conditions in 2014. An additional survey was conducted in May 2015, following an accidental sulphuric acid spill above the Sewage Treatment Works (STW). Significant linear correlations were identified between physico-chemical parameters and the indices, as well as between the three indices themselves, validating their use to infer water quality. Water quality deteriorated from the source of the Klein Nyl River, especially at the STW, but improved within the Nylsvley Nature Reserve wetland sampling site (NYL).

A Multivariate Analysis of Metal Concentrations in Two Fish Species of the Nyl River System, Limpopo Province, South Africa.

Increased toxicity due to high metal concentrations may hinder the ecological integrity of aquatic ecosystems in sustaining life. The non-biodegradable nature of metals may result in bioaccumulation in aquatic organisms. Due to ecological and social aspects it is imperative for monitoring schemes to identify possible impacts to the systems integrity. This paper discusses accumulation patterns of seven metals (Al, Cr, Cu, Fe, Mn, Sr and Zn) in tissues of two fish species, namely Clarias gariepinus and Oreochromis mossambicus at two selected sites, the first located upstream of Modimolle (NRS1), and the second located downstream of the town (NRS2). Gills, liver, muscle and skin tissues were analysed for metal concentrations using standard microwave digestion and inductively coupled plasma mass spectrometry techniques. Statistical results indicated higher concentrations of metals at NRS2 in comparison to NRS1, indicating that Modimolle plays a potential role in introducing metals into the aquatic system.

Ecological risk assessment of trace elements in sediment: A case study from Limpopo, South Africa

This study aimed to determine the ecological risk posed by metals, in sediments from the Nyl River system in Limpopo, South Africa. Metals were extracted from sediment samples by aqua regia microwave digestion and were analysed using standard ICP-OES techniques. The ecological risk indices applied to the data included Contamination Factor, Pollution Load Index, Geo-accumulation Index and Enrichment Factor. The results showed that the levels of Ni at STW and NYL in the HF period exceeded the Canadian Sediment Quality Guidelines by a factor of 1.36 and 1.83 respectively whereas NYL and MDD had 2.57 and 1.32 times the allowed limit of Ni in the LF period. During the HF period, the GC site exceeded the allowed limit of Zn by a factor of 1.04 and NYL had 1.21 times the allowed Zn in the LF period. The levels of metals are generally low near the origin of the river and increase moving downstream. The levels of metals in the Nyl River floodplain, a Ramsar accredited wetland, were high with CF scores ranging between 0.905 and 5.82, Igeo values with a range of −0.541 to 2.441 and EF scores ranging from 0.959 to 6.171. and posed a greater risk than the other sites. This indicated that the wetland is performing its ecological function by trapping and removing toxins from the water body. The Pollution Load Index determined that the Golf Course (PLI=4.586) and STW (PLI=2.617) sites were polluted only in the low flow period whereas the Nyl River floodplain (HF PLI=79.845; LF PLI=30378.768) and Moorddrift Dam (HF PLI=1.903; LF PLI=9.256) sites were polluted in high flow and low flow periods.

Heavy metal concentrations in the water of the Nyl River system, South Africa

The Nyl River floodplain, a Ramsar site that provides habitat for a number of endangered species, is one of the jewels in the arid Limpopo province and thus its conservation and protection are vitally important. Very little work has been done on assessing its water quality and no data have been published on the metal concentrations found in this valuable system. The aim of this project was thus to provide baseline data for metal concentrations in the Nyl River floodplain system and to determine whether there were any point sources of pollution or if its metal levels were natural. Eighteen localities along the course of the Nyl River were selected as sampling sites. Water samples were collected quarterly, between August 2001 and July 2002, and analysed using ICP-MS to determine metal content. Zinc, copper, iron, selenium, cadmium, lead, aluminium, arsenic, chromium and manganese concentrations were determined. Although metal concentrations in the water were greater than target water quality range (TWQR) values for aquatic ecosystems, they remained relatively constant throughout the system and posed little or no potential threat to the system. The results suggest that the metal content originates from natural sources.

A preliminary survey of biotic composition of the Olifantspruit catchment, South Africa

As a major tributary of the Nyl River, and ultimately for the Nylsvley wetland, the Olifantspruit, Limpopo province, South Africa, was investigated during the summer (high flow) and winter (low flow) of 2007 at three sites. This preliminary study used physical and biological indicators to determine the quality of the water that ultimately flows into Nylsvley. Significant seasonal differences were found. The observed differences relate to habitat structural differences and human activities in the catchment. Key findings included higher water temperatures during the high-flow period than during the low-flow period. The higher temperatures were accompanied by lower concentrations of dissolved oxygen at all sites. In total, 13 fish species were recorded, with most being found in the pool biotopes. The Nantes site, located nearest to the Nylsvley wetland, had the highest number of fish species, possibly indicating a linkage between these two systems. The most common macroinvertebrate families were the Baetidae, Aeshnidae and Coenagrionidae. It can be assumed that this river acts as an important refuge area for fish and macroinvertebrates from the Nyl River, and therefore it is important to conserve the Olifantspruit.

The spatial and temporal characterisation of flooding within the floodplain wetland of the Nyl River, Limpopo Province, South Africa

The inundated area of a wetland is characterised by annual and interannual variability. This paper presents remotely-sensed imagery in order to better understand the spatial and temporal patterns of flooding within the floodplain wetland of the Nyl River, Limpopo Province. A detailed understanding of the hydrological characteristics of these flood events is essential in order to develop sustainable ecological and hydrological management plans for the area. From the results, flooding is shown to occur in 2 distinct phases. The initial phase is characterised by water ponding on the floodplain. The later phase is characterised by the input of water from tributaries to the north (e.g. Andriesspruit and Tobiasspriut) and southwest (e.g. Klein Nyl and Groot Nyl). This distinction may relate to the increasingly widespread practice of agricultural irrigation within adjacent tributary catchments. The methodology described in this study could yield valuable results when applied to other wetland systems in southern Africa.

The origin and development of the Nyl River floodplain wetland, Limpopo Province, South Africa: trunk–tributary river interactions in a dryland setting

The Nyl River floodplain wetland, one of South Africa's largest floodplain wetlands and a Ramsar site of international conservation importance, is located in an area of long-term and still active valley sediment accumulation. Creation of accommodation space for sedimentation has previously been attributed to tectonic controls, but new investigations reveal that a more likely cause is progradation of coarse-grained tributary fans across the narrow river valley downstream of the main area of floodplain wetland. Obstruction of trunk river flow and sediment transfer by these tributary fans has led to backponding and upstream gradient reduction and to accumulation of valley fills up to ∼35 m thick. Chronological control for the timing and rate of sediment accumulation is limited, but we hypothesise that a semi-arid to arid climate, characterised by asynchronous trunk–tributary activity that results in marked discontinuities in downstream water and sediment transfer, is likely to have been a key control. These interpretations are supported by other studies of dryland rivers globally and the findings add to our growing understanding of the controls on the origin and development of southern African wetlands, particularly by demonstrating how the combination of a particular physiography and a dryland climate can impart some distinctive geomorphological characteristics.

Bacterial levels in the Nyl River system, Limpopo province, South Africa

Because water quantity and quality are of great importance in the arid Limpopo province, the bacterial content of water in the Nyl River System and its possible origins were assessed at five sites. Quarterly surveys took place between April 2001 and July 2002 and the water was analysed for bacterial counts using standard procedures. Heterotrophic plate counts, faecal coliform counts and total coliform counts indicated that the system was stressed. The Modimolle sewage treatment works and local agricultural activities were found to be the point and diffuse sources of bacterial contamination, respectively.

The character, origin and palaeoenvironmental significance of the Wonderkrater spring mound, South Africa

Wonderkrater is a spring mound consisting entirely of peat in excess of 8 m thick. It has yielded a pollen record extending back over 35,000 years, which has provided one of the very few proxy climatic records for the interior of southern Africa in the Late Pleistocene and Holocene. The current investigation of the morphology and sedimentology of the site has revealed that the peat mound formed due to artesian conditions at the spring, but that accumulation of the thick peat succession was made possible because of clastic sedimentation on the surrounding piedmont which in turn was brought about by aggradation on the adjacent Nyl River floodplain. The peat mound has remained elevated relative to the surrounding piedmont for most of the 35,000 year period. Aggradation of the mound was slower during the Late Pleistocene than the Holocene (0.06–0.1 m/1000 year and 0.2–0.38 m/1000 year, respectively). Controlled archaeological excavations yielded a diverse late Pleistocene fauna preserved in peat and sand in the mound. A 1 m thick, coarse sand horizon at the base of the peat deposit contained a rich Middle Stone Age (>30 k year) lithic assemblage. The MSA sand layer likely represents an arid phase, suggesting the site’s antiquity as a place of refuge for Quaternary animals and the people that hunted them.

Hydrologic and hydraulic modelling of the Nyl River floodplain Part 3: Applications to assess ecological impact

The ecological functioning of the Nyl River floodplain in the Limpopo Province of South Africa depends on water supplied by catchments which are experiencing continuing water resource development. Hydrological and hydraulic models have been produced to assist in future planning by simulating the effects of developments on ecologically relevant flooding characteristics. The models are applied here to predict the impacts of different development scenarios on the areal extent of suitable habitat for a key species, the Wild Rice (Oryza longistaminata), which can be characterised in terms of the depth, duration and timing of flood events. The results show that historical developments in the contributing catchments have already significantlyreduced the area suitable for Wild Rice growth, particularly in relatively dry years, and increased the likely dry period between flooding events. Dam construction on one of the tributaries would reduce the suitable area further in dry to average years and increase the inter-event dry period. Careful dam operation could ameliorate impacts in very dry years, however.

Hydrological and hydraulic modelling of the Nyl River floodplain Part 2: Modelling hydraulic behaviour

Catchment land-use and water resource developments may threaten the ecological integrity of the Nyl River floodplain, a world-renowned conservation area. The effect of developments on the water supply regime to the floodplain can be predicted by hydrological modelling, but assessing their ecological consequences requires transformation of discharge into ecologically-relevant hydraulic characteristics. Studies of Wild Rice (Oryza longistaminata) have indicated that the important variables are the extent, depth, duration and timing of flood inundations. One-dimensional hydraulic modelling has been successfully applied to predict these flood characteristics, using a suite of models comprising Quicksurf, RiverCAD, HEC-RAS and HEC-DSSVue. Separate but linked models were developed for three contiguous portions of the large floodplain. The topography was surveyed by airborne laser mapping, and extensive discharge, water level, rainfall, infiltration and evapotranspiration data were collected for model calibration and verification. The models were successfully calibrated through adjustment of Manning’s n for the main channel and floodplain in each portion, and are able to predict flooding characteristics at a resolution appropriate for ecological interpretation

Hydrological and hydraulic modelling of the Nyl River floodplain Part 1. Background and hydrological modelling

The Nyl River floodplain is a seasonal wetland of great conservation importance in Limpopo Province, South Africa. Water resource developments in the upstream catchments are changing the quantity and timing of water delivery to the floodplain, and this is expected to have an ecological impact. Hydrological and hydraulic models have been developed to help assess this impact. This paper describes the calibration and application of hydrological models of the contributing catchments. The hydraulic modelling and scenario applications to predict changes to vegetation habitat associated with upstream developments are presented in two companion papers. Hydrological simulations were performed using two models, one using daily time steps and the other using monthly time steps. The models were calibrated using historical data on 10 gauged catchments. Their performance was similar in producing average monthly and annual flows, although the higher resolution daily model agreed more closely with the historical data. Simulated estimates of mean annual runoff values for individual catchments compared well with results from previous studies. The daily model also predicted acceptable measures of probability distributions of maximum annual daily flows and daily flows exceeding a specified threshold.

NOTES ON THE NATURAL HISTORY OF A TRAPDOOR SPIDER ANCYLOTRYPA SIMON (ARANEAE, CYRTAUCHENIIDAE) THAT CONSTRUCTS A SPHERICAL BURROW PLUG

Burrows of an unidentified species of Ancylotrypa Simon from the floodplain of the Nyl River in Limpopo Province, South Africa are described. In addition to constructing a thin trapdoor, members of this species construct a hard, spherical plug or marble from soil particles held together with silk. Burrow structure, the plug and associated behavior are described for the first time.

Nutrient-reserve dynamics of semiarid-breeding White-faced Whistling Ducks: a north-temperate contrast

Little is known about the nutrient-reserve dynamics of waterfowl that breed in semiarid environments. Breeding White-faced Whistling Ducks, Dendrocygna viduata (L., 1766), were collected on the Nyl River floodplain, South Africa, during 1992–1993 and 1995. Mass of major lipid (wet skin + visceral fat + abdominal fat) and protein (breast muscle + leg muscle + gizzard) deposits and organs of males and females were evaluated in relation to sex and reproductive stage. Both sexes arrived at breeding areas with large lipid reserves and did not store additional lipid after arrival. Stored reserves enabled females to begin laying shortly after arrival, an important adaptation to ephemeral wetlands in semiarid environments. Females catabolized at least 37 g of lipid and 27 g of body protein during rapid follicular growth and ovulation. This accounted for 87% of their total lipid and 60% of their protein requirements during egg laying. Males catabolized at least 19 g of lipid between arrival and the end of laying. Although diets of breeding White-faced Whistling Ducks are high in fat, females satisfied most of their lipid requirements for clutch formation from endogenous reserves. Female White-faced Whistling Ducks can reproduce despite their reliance on a relatively low protein diet, and this suggests that they efficiently assimilate amino acids from plant matter. Biparental care apparently decreases the reliance of female White-faced Whistling Ducks on stored nutrients after ovulation, thereby allowing greater allocation of stored nutrients to egg production.

THE GEOMORPHOLOGY OF THE NYL RIVER AND FLOODPLAIN IN THE SEMI-ARID NORTHERN PROVINCE, SOUTH AFRICA

ABSTRACT The Nylsvlei wetland is located on the 240 km2 floodplain of the lower Nyl River in the semi-arid Northern Province. The wetland is supplied seasonally with water and sediment by the Nyl and other small tributaries but has been little studied geomorphologically. The Nyl floodplain has formed within a basinal to synclinal structure on the downthrown side of a fault and the variable stratigraphy influences both ground and surface water flows, and the resultant fluvial landforms and ecology. Owing to downstream decreases in discharge and channel-bed gradient, the Nyl and several other tributaries presently decrease in size downstream and disappear at the margins of the floodplain, such that summer flooding occurs primarily as sheetflow. Thin clay layers deposited by these sheetflows effectively seal the floodplain surface, prolonging inundation and limiting groundwater recharge. Some groundwater recharge, however, occurs by floodwater infiltration through the channel beds of gravelly sand at the floodplain margins. Groundwater supply may contribute to growth of the numerous elevated, circular, floodplain islands which are characterised by woody fringes but sparsely-vegetated interiors. At the downstream end of the floodplain, bedrock outcrop induces convergence of the rare floodwaters and, together with a steepening of gradient, results in a well-defined channel again forming (Mogalakwena River). Correct identification of the factors giving rise to such wetlands, and the hydrogeomorphological processes governing their development, provides an essential context for long-term ecological studies as well as information for the design of effective management guidelines for these fragile habitats.

Aftermath of simultaneous toxic spills in the Klein Nyl River, Northern Province, South Africa

In late August 1998, a mechanical malfunction at the Nylstroom Sewage Treatment Works resulted in a massive quantity of untreated sewage flowing into the Klein Nyl River. Simultaneously, 5km upstream, a poly-aromatic hydrocarbon poison was simultaneously leaked into the same river from a 25 litre canister. These spills threatened the Nylsvley Nature Reserve, a newly acclaimed RAMSAR site, situated about 20km downstream of Nylstroom. The Limnological team of the Department of Zoology, University of the North, was asked to assist with the assessment of the effect of these spills, which resulted in a massive fish kill. A monitoring program was implemented in early September 1998 to assess the effect of these spills on the water quality of the receiving water body. The implications of the altered water quality on the aquatic biota are discussed.

Metabolic Rate, Temperature Regulation, and the Energetic Implications of Roost Nests in the Bananaquit (Coereba flaveola)

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