Wetland Health and Importance Research Programme Aquatic Invertebrates as Indicators of 3 Human Impacts in South African Wetlands T T 4 3 5 / 0 9 W e t l a n d H e a l t h a n d I m p o r t a n c e R e s e a r c h P r o g r a m m e – 3 Author: M Bird Series Editor: H Malan TT 435/09 WETLAND HEALTH AND IMPORTANCE RESEARCH PROGRAMME AQUATIC INVERTEBRATES AS 3 INDICATORS OF HUMAN IMPACTS IN SOUTH AFRICAN WETLANDS Report to the Water Research Commission by Author: M Bird Series Editor: H Malan Freshwater Research Unit, University of Cape Town WRC Report No. TT 435/09 March 2010 OBTAINABLE FROM Water Research Commision Private Bag X03 Gezina, 0031 The publication of this report emanates from a project entitled Wetland Health and Importance Research Programme (WRC Project no. K5/1584). DISCLAIMER This report has been reviewed by the Water Research Commission (WRC) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. ISBN 978-1-77005-927-6 Set No. 978-1-77005-936-8 Printed in the Republic of South Africa Front Cover: A seasonal wetland from the Rondevlei Nature Reserve, Cape Town, South Africa Inset: A Culicid larva (mosquito) Photographs: M Bird i PREFACE This report is one of the outputs of the Wetland Health and Importance (WHI) research programme which was funded by the Water Research Commission. The WHI represents Phase II of the National Wetlands Research Programme and was formerly known as “Wetland Health and Integrity”. Phase I, under the leadership of Professor Ellery, resulted in the “WET-Management” series of publications. Phase II, the WHI programme, was broadly aimed at assessing wetland environmental condition and socio-economic importance. The full list of reports from this research programme is given below. All the reports, except one, are published as WRC reports with H. Malan as series editor. The findings of the study on the effect of wetland environmental condition, rehabilitation and creation on disease vectors were published as a review article in the journal Water SA (see under “miscellaneous”). An Excel database was created to house the biological sampling data from the Western Cape and is recorded on a CD provided at the back of Day and Malan (2010). The data were collected from mainly pans and seep wetlands over the period of 2007 to the end of 2008. Descriptions of each of the wetland sites are provided, as well as water quality data, plant and invertebrate species lists where collected. An overview of the series Tools and metrics for assessment of wetland environmental condition and socio- economic importance: handbook to the WHI research programme by E. Day and H. Malan. 2010. (This includes “A critique of currently-available SA wetland assessment tools and recommendations for their future development” by H. Malan as an appendix to the document). Assessing wetland environmental condition using biota Aquatic invertebrates as indicators of human impacts in South African wetlands by M. Bird. 2010. The assessment of temporary wetlands during dry conditions by J. Day, E. Day, V. Ross- Gillespie and A. Ketley. 2010. ii Development of a tool for assessment of the environmental condition of wetlands using macrophytes by F. Corry. 2010. Broad-scale assessment of impacts and ecosystem services A method for assessing cumulative impacts on wetland functions at the catchment or landscape scale by W. Ellery, S. Grenfell, M. Grenfell, C. Jaganath, H. Malan and D. Kotze. 2010. Socio-economic and sustainability studies Wetland valuation. Vol I: Wetland ecosystem services and their valuation: a review of current understanding and practice by Turpie, K. Lannas, N. Scovronick and A. Louw. 2010. Wetland valuation. Vol II: Wetland valuation case studies by J. Turpie (Editor). 2010. Wetland valuation. Vol III: A tool for the assessment of the livelihood value of wetlands by J. Turpie. 2010. Wetland valuation. Vol IV: A protocol for the quantification and valuation of wetland ecosystem services by J. Turpie and M. Kleynhans. 2010. WET-SustainableUse: A system for assessing the sustainability of wetland use by D. Kotze. 2010. Assessment of the environmental condition, ecosystem service provision and sustainability of use of two wetlands in the Kamiesberg uplands by D. Kotze, H. Malan, W. Ellery, I. Samuels and L. Saul. 2010. Miscellaneous Wetlands and invertebrate disease hosts: are we asking for trouble? By H. Malan, C. Appleton, J. Day and J. Dini (Published in Water SA 35: (5) 2009 pp 753-768). iii EXECUTIVE SUMMARY RATIONALE The importance of wetland habitats for various human concerns and as a critical store of biodiversity is now recognised on a worldwide scale. Traditionally, research and conservation attention has been centred on rivers and lakes and only relatively recently has the focus shifted to wetlands. The recent emphasis on wetland protection and management has created an urgent need to develop assessment tools to establish and monitor human impacts in wetland ecosystems so as to prioritise wetlands for conservation and rehabilitation actions and to monitor the effects of these actions. Biological assessment or “bioassessment” is one of the means of investigating wetland condition and involves the evaluation of ‘a wetland’s ability to support and maintain a balanced, adaptive community of organisms having a species composition, diversity and functional organisation comparable with that of minimally disturbed wetlands within a region’ (DWAF, 2004, adapted from Karr and Dudley, 1981). Potential indicator groups for bioassessment purposes include macrophytes, algae and diatoms, aquatic invertebrates, birds and fish. Macrophytes emerge as the most popular biotic assemblage for use in wetland bioassessment worldwide and the ecology and functioning of wetland plants is relatively well understood in comparison to other biotic assemblages inhabiting wetlands (Adamus et al., 2001; DWAF, 2004). Aquatic invertebrates are regarded as the second most useful group for wetland bioassessment worldwide (Adamus and Brandt, 1990; Butcher, 2003; DWAF, 2004), although their ecological and functional roles in wetland ecosystems are not well understood. The topic of this study centres on the use of aquatic invertebrates as a bioassessment tool for inland wetlands in South Africa. Marine (open ocean) and estuarine wetlands (connected to the sea) are not covered in this report. Successful wetland bioassessment programmes using aquatic macro-invertebrates have been developed and implemented in parts of the USA (Helgen, 2002), suggesting their beneficial use for bioassessment in other parts of the world. In South Africa, a method of assessing and monitoring wetland condition is required in order to meet national legislative requirements (National Water Act No. 36 of 1998). The Wetland Health and Importance (WHI) Research Programme was launched in April 2006 by the Water Research Commission (WRC) under Phase II of the National Wetland Research Programme. This study investigates the feasibility of using invertebrates in the bioassessment of wetlands and forms one of the components of the WHI. iv STUDY OBJECTIVES The objectives of this study were to:  collate and review both local and international literature relating to wetland biological assessment using aquatic invertebrates;  conduct an investigation into the response of aquatic invertebrates (including micro- crustaceans) to anthropogenic disturbances in isolated depression wetlands of the Western Cape, South Africa;  identify candidate invertebrate taxa or metrics for assessing human impacts on isolated depression wetlands in the Western Cape; and if useful indicator taxa and/or metrics are established, to provide a protocol for developing an assessment method using aquatic invertebrates; and  investigate the applicability of the SASS river index to wetlands; in this regard, both lentic (e.g. isolated depressions) and lotic (e.g. valley bottom) wetland types will be investigated. DOCUMENT STRUCTURE This report is divided into two major components: Component 1 is the literature review, which provides an overview of biological assessment techniques in rivers and wetlands. The focus is on collating state-of-the-art information on biological assessment of wetlands using invertebrates worldwide and presents the various potential options for use in South Africa; and Component 2 is the empirical research undertaken in this study. The key facets of this component are: a) an exploratory analysis of quantitative relationships between aquatic invertebrates and human disturbance variables in Western Cape isolated depression wetlands; b) investigation of potential index options for future use in this wetland type and discussion of applicability in other areas and wetland types; v c) investigation of SASS index applicability in isolated depression wetlands of the Western Cape; and d) investigation of SASS index applicability in valley bottom wetlands of the Western Cape in order to clarify whether SASS is a valid protocol for slow flowing wetlands. STUDY APPROACH The empirical research component of this study involved sampling 125 isolated depression wetlands spread across the Western Cape winter rainfall region as well as a set of valley bottom wetlands in the greater Cape Town area. These two wetland types were chosen based on their abundance in the region and suitability for addressing the objectives of this study. The isolated depression wetlands were sampled for aquatic invertebrates and various human disturbance variables (water column nutrient levels and a rapid assessment index of human landscape disturbance) in order to relate human impairment with invertebrate assemblage composition and abundance patterns. The collected data were used to:  develop a multi-metric Index of Biological Integrity (IBI) and to investigate feasibility of such an index for the given wetland type;  test the SASS index in terms of its ability to distinguish differential levels of wetland impairment; and  develop a numerical biotic index approach similar to SASS, but with modifications for use in this specific wetland type. The indices developed for isolated depression wetlands during the empirical research component of this report were further tested using a dataset provided by De Roeck (2008) in order to validate their ability to classify an independent set of wetlands in terms of landscape disturbance and trophic status (proxied by nutrient levels). Fifteen valley bottom wetlands were sampled using a modified SASS sampling protocol and SASS ASPT scores were compared among nutrient enrichment and landscape disturbance categories so as to test correspondence between observed impairment and SASS scoring for this wetland type. vi MAJOR FINDINGS Literature review The body of literature on wetland bioassessment protocols using aquatic invertebrates is small and centred almost entirely on research conducted in the USA and Australia in the last 10-15 years. Wetland invertebrates possess a number of advantageous attributes as biological indicators of disturbance. The majority of published findings in the literature suggest aquatic macro-invertebrates as a beneficial tool for the biological assessment of wetlands, but indices need to be modified, sometimes significantly so, in order to be used in different eco-regions of the same country. With the latter point in mind, river macro- invertebrate indices appear to hold an advantage of often being applicable over broad spatial areas with little or no modification to indices. Certain studies (e.g. Tangen et al., 2003) indicate that aquatic macro-invertebrates are not a feasible tool for wetland bioassessment in areas where the influence of natural environmental disturbances outweigh anthropogenic-induced disturbances (e.g. areas with extreme climatic fluctuations between seasons). Other potential pitfalls in developing macro-invertebrate indices for wetland bioassessment include the lack of empirical information on responses of invertebrates to human stressors and the dearth of taxonomic information for making correct identifications of wetland taxa. The use of micro-crustacean taxa could add an important complement of information to the more traditional macro-invertebrate assessment techniques, but is likely to be significantly hindered by the difficulties involved in identification and enumeration of such taxa, which may preclude rapid assessment methods from being developed. Empirical component: isolated depression wetlands Indicator taxa – macro-invertebrates The majority of macro-invertebrate families sampled during this study showed a generalist pattern of response to the human disturbance variables, in that these families seem to tolerate a wide range of human-imposed disturbance conditions. Fourteen families were described in this manner as ‘generalists’, whereas 11 families showed some observable response to human impairment. A considerable number of families appear to be very localized in their distributions (15 families were present in <5% of sites) and were too rare for the purpose of deducing patterns. Those families for which vii relationships to human disturbance variables were found, tended to have weak patterns of association in relation to comparable studies in the literature. Indicator taxa – micro-crustaceans Only 7 of the 50 micro-crustacean taxa identified from this study showed potential as indicators of human disturbance. Of these, only 3 taxa (Metadiaptomus purcelli, Zonocypris cordata and Daphnia pulex/obtusa) showed good patterns with reliable sample sizes. The majority of taxa analyzed against human disturbance variables showed a typically generalist-type response and would not be of any particular use for bioassessment purposes. Almost half the taxa (22) were too rare for analysis (present in less than 5% of sites), indicating that their distributions are most likely too localized for use in a bioassessment index. An important point to stress when it came to micro- crustaceans is that the difficulties encountered in getting reliable identifications considerably outweighed the usefulness of the results obtained for bioassessment purposes. Testing metrics – macro-invertebrates As observed with macro-invertebrate families, relationships between metrics (summary measures of macro-invertebrate community composition) and human disturbance variables were not particularly strong and the power to infer wetland condition was low in comparison to published metrics. A multi-metric IBI (Index of Biological Integrity) was developed using a set of the most optimal metric results from this study, but regressions of total IBI scores with human disturbance variables proved weak and had low inferential power. Testing metrics – micro-crustaceans Thirteen metrics were assessed using micro-crustaceans, but provided little information for bioassessment purposes. Relationships were weak between metrics and human disturbance variables and produced only two feasible metrics (% Copepoda and % Ostracoda), both of which had low inferential power and would be expected to suffer from a reasonably high error rate.