Water for Ecosystems | The Water Page

This feature on water for ecosystems consists of a short review article introducing the topic and providing some background, plus a list of useful hard-copy references and web-based documents. The feature will stay “live” for as long as the issue of water for ecosystems is topical (it’s a very hot issue right now in the water field) – as new information becomes available we will update the links and references.Water for ecosystems is a fairly new issue, and scientific research in the field has only been really active for about the last 10 years. While there is quite a body of work reported in the scientific literature, the issue is only just beginning to surface in policy and law worldwide, and as yet there have been very few cases of real implementation of water allocations for aquatic ecosystems.The Contracting Parties to the Ramsar Convention have recognised the issue of water for ecosystems to be important, and guidelines on management of water allocations for wetland ecosystems are currently being drafted for possible adoption at the next Conference of Parties. The report of the World Commission on Dams strongly supports the determination of environmental water requirements and incorporation of these requirements into the operating rules of dams. Principles and guidelines are provided in their report (see below for link).Aquatic ecosystems take many shapes and forms. At the largest scale, a whole river catchment from the mountains to the sea is a single ecosystem by itself, linked to other catchment ecosystems through terrestrial corridors, atmospheric corridors and subterranean corridors. Usually however this is too large a scale for everyday operations, though it is useful for planning to think of a catchment as a whole ecosystem. Generally in water resources management, we identify and delineate smaller units as ecosystems. An ecosystem could be the size of the Okavango Delta, and in pristine condition or nearly so. An ecosystem could be the estuarine reaches of a river, or it could be a pan which receives only rain water, or a spring which is fed by groundwater. Some aquatic ecosystems can be entirely subterranean, such as the karst systems or those found in unconstructed aquifers. Aquatic ecosystems do not have to be unimpacted to have ecological value – urban rivers and water resources provide important green corridors and recreational areas, and have high amenity values for city dwellers, including transport, flood control, processing of biodegradable wastes and provision of water supply.An ecosystem, whatever form it takes, is usually characterised by the ecological processes which occur within it and between that ecosystem and other neighbouring ecosystems. All the elements of the food chain should be present, including primary producers (single-celled organisms such as plankton), grazers (invertebrates), predators (from macrofauna such as shrimps through to tiger fish or crocodiles), and organisms such as bacteria which process waste products of the food chain back into material which the primary producers can consume. Sufficient suitable habitat (hydraulic habitat, physico-chemical habitat and geomorphological habitat) should be available for each member of the food chain to find a living space within which they can carry out their normal daily and seasonal functions. Ecosystem functions are crucial to human life. They provide many critical services to humans, such as:Plants (both macrophytes and algae) carry out photosynthesis & production of oxygen;Bacteria process organic waste products and maintain good water quality;Riparian vegetation mitigates floods and provides more stable river and spring flows;More reliable flow regimes can be utilised for food production, transport, water supply or to support terrestrial ecosystems and wildlife;Healthy ecosystems ensure maintenance of biodiversity and hence resilience to the pressures of utilisation.We don’t have to maintain all aquatic ecosystems in pristine states to enjoy the benefits of these services – a healthy ecosystem with all the main components of habitat and food chain present will continue to provide selected functions which we can rely upon. The general rule is, the more natural the ecosystem, the more diverse the range of functions we can expect, but sometimes we want to concentrate on just a few of the ecological functions and so we manage the ecosystem for that e.g. if we manage an urban river primarily to remove flood waters, then we may not be too worried about providing habitat for invertebrates, but we would want the riparian vegetation and the banks to be in a good state and not be eroding or unstable. Another rather extreme example is that of an oxidation pond, where we encourage excessive growths of algae and of the bacteria which decompose waste, in order to process as much waste as possible, without being concerned about whether the water is also safe for swimming or for fish.Because we don’t know what the next generation of people may need or want to get from ecosystems in terms of services, sustainability principles say that we should not rule out options for the future, i.e. we should not reduce the potential array of services which future generations may wish to access from an ecosystem. So when making management decisions, we should be trying to maintain aquatic ecosystems in as natural a state as is possible and practical, in order to maintain the potential for a diverse array of ecosystem functions and services. In many other countries (e.g. Germany) we see rivers which have been canalised and reduced to very artificial systems being returned to as natural a form as possible, in order to regenerate some of the ecosystem functions and services which have been lost over the centuries.As “renewable natural resources”, water resources have a certain amount of resilience to the pressures and demands of utilisation by humans, since they are used to a certain amount of natural variability anyway. This resilience allows water resources to be utilised on a continuous basis, as long as the demands are not too great. However, if a water resource is over-utilised or allowed to degrade too far, (i.e. too much water is taken out, too much waste is put in, natural shape and structure are modified too greatly by erosion, sedimentation or habitat degradation), then the water ecosystem loses resilience and begins to break down. The ecological integrity of the resource can be damaged: once this happens, the capability of the resource to meet people’s demands for utilisation can be reduced, or possibly even lost altogether. If the utilisation of water resources remains at a level within the limits which can protect ecological resilience, then that level of utilisation can be sustained indefinitely.The water in an aquatic ecosystem is to the ecosystem as the air we breathe is to us. Aquatic organisms need water to provide habitat for them so that they can carry out their usual functions and provide the services we are used to: the water needs to be deep enough to fill pools and pans, or spill over rapids to provide fast-flowing, highly-oxygenated habitats, or recharge groundwater to provide saturated zones for plant roots or for specially adapted fauna. Water needs to be present or absent at the right times of the year: many organisms are adapted to expect a series of small floods (called freshets) at the beginning of the rainy season which signals to them that it is time to breed, before the bigger mid-season floods arrive. Migratory estuarine species need small pulses of freshwater to signal the start of migration and to provide direction. Some ecosystems are adapted to need flows to dry up completely each dry season – others cannot survive unless a certain amount of water is present in the dry season.Of course, if the water is not of the right quality, aquatic ecosystem functions may also be compromised. For example, some ecosystems are adapted to water of naturally low pH due to the underlying geology: if the water becomes more alkaline due to discharge of factory effluents or perhaps leaching of salts from irrigated soils, this will affect the aquatic organisms. The more sensitive organisms may be lost from the system, along with the ecological functions that they support. If too much organic waste is put into a system, the bacteria which decompose waste may not be able to cope with the load: oxygen levels in the water may drop too low and only the toughest organisms (such as algae or catfish) can survive.It is especially important to note that the water allocation to a water resource or to an aquatic ecosystem is not just the minimum water quantity and water quality required for protection of that ecosystem and its functions. For a water resource which is classified as being of high protection status, the water allocation would be set at a higher level, which would correspond to the idea of minimum risk and maximum caution. For a water resource which is assigned lower protection status, the allocation would be set at a level which should still afford protection to the resource, but without the benefit of the buffer which caution provides. The idea of classification of aquatic ecosystems according to protection status is developing worldwide, and a good example of a typical classification system can be found in the EU Water Framework Directive (see below for hyperlink).Yet to assume that a “higher” allocation necessarily means that only a greater quantity of water is allocated to protection of the resource is somewhat simplistic. The assurance or reliability of water, especially under extreme climatic conditions, is just as critical an aspect of the allocation as the quantity and quality.Available habitat is normally used as the basis for a determination of the water requirements of aquatic ecosystems. Surveys are undertaken to ascertain what ecological type of system is being dealt with, which representatives of all the trophic levels (levels in the food chain) are present and which are the important ecological cues or signals which must be provided by certain flows at certain times of the year. Ecologists can then make recommendations regarding what kinds and extent of habitats should be maintained i.e. sand, rocks, pools, riffles and runs, what flows are needed during the year to provide these habitats and what flow depths and velocities are needed in the river or estuary at representative control points. These habitat requirements are then translated into flows which must be released from a dam upstream or which must be present in the river at flow monitoring points after all offstream abstractions have been made. A modified flow regime is designed which will maintain certain selected ecosystem functions. The closer to natural this flow regime is, the more of the natural ecosystem functions can be retained.Water quality requirements are also set on the basis of providing suitable habitat for aquatic organisms to grow through all life stages, feed and reproduce. Organisms which represent each trophic level are tested in the laboratory to determine what their tolerances are to different concentrations of the major water quality constituents, and how different concentrations of these constituents can affect growth, breeding and development. Concentrations which cause chronic and acute toxicity effects in various species of aquatic organisms are identified. Safe water quality levels are determined which will provide adequate protection for all the levels of the food chain – sometimes these levels are set very stringently (such as the No Observed Effects Level), at other times more risk of adverse effects on aquatic organisms may be accepted in order to allow more impacts of utilisation by humans.Since aquatic ecosystems are each unique, in hydrological, biophysical and ecological terms, water allocations which are set for one ecosystem can very seldom be applied directly to another ecosystem, even one of the same ecological type. Natural site-specific differences must be taken into account. It is the concepts of levels of risk, and levels of protection, which are generally applicable, rather than numerical objectives themselves. In only a few cases (such as for persistent toxic substances) would it be practical to set numerical objectives which would be applicable to all water resources of a particular class or protection status wherever they were geographically located. For example, a concentration of a substance which poses only a slight risk to a particular ecosystem in one geographical region may result in a much higher risk in another geographical region, depending on the resilience of the adapted ecosystem, the background quality of the water, and the natural flow regime.Although there are very few numerical objectives, for water quantity or water quality, which would be generally applicable to all ecosystems, there are generic processes available for determining site-specific water quantity and quality requirements. A range of such processes has been developed over recent years, as there has been a growth in research into methods for determination of “environmental flows”.In keeping with the ecosystem approach, any generic process to determine water allocations for aquatic ecosystems should be consistent the principles of integrated environmental management. Recommended design specifications for methodologies to determine water allocations for aquatic ecosystems include:that they be legally defensible, since they must serve as a basis for control and management of impacts and for issuing legally valid water use authorizations and licenses (test the approaches with legal experts or involve legal people in method development);that they be scientifically defensible, and based on sound ecological principles in line with the integrated ecosystem approach to water resource management (use best available scientific knowledge and ensure wide input and discussion of the methods with scientists during development);that they match administrative requirements, i.e. that the information be provided to the water resource management agencies in a format which can be used as a basis for drawing up water use allocation plans and catchment management strategies, and for setting individual water use license conditions (establish licensing processes and the proposed license format early on, and use this as a guide to design the output from methods to determine water allocations for aquatic ecosystems);that they provide conservative estimates of the water quantity and quality required to provide the water allocation for a wetland ecosystem, in line with the precautionary principle;methodologies should be derived from available technologies and understanding in the region where the wetland ecosystem is situated, since that will give confidence in the scientific validity and acceptance, and also there is likely to be more specialist capacity available to implement procedures or approaches which are already in use. Preferably these technologies should have been published in the scientific literature.methodologies should utilise a holistic ecosystem endpoint, rather than a purely hydrological one or a purely chemical one.Rapid methodsThere are many rapid methods available for estimation of water allocations for wetland ecosystems (Tharme, 1996). (“Rapid” means at a desktop level.) Most of these methods are based on the establishment of an empirical relationship between the flow in a river or channel (as water volume per unit time), and the resulting structure and function of the associated aquatic ecosystem. These methods generally require hydrological data for virgin and present-day runoff, with at least annual resolution. Some methods attempt to provide greater accuracy by linking various hydrological statistics to ecosystem structure and function, but in either case the methods are usually subjective and provide only coarse answers, at the resolution of annual volumes, or average monthly flows. Neither annual nor monthly resolution is sufficient for actually managing flow releases for wetland ecosystems, but this kind of information can be very useful in planning at the macro scale.One of the best-known rapid methodologies is the so-called “Montana method” (Tennant, 1976), in which the proportion of the virgin mean annual runoff provided to a river ecosystem can be related empirically to the ecological condition of that ecosystem. This methodology relies on observations of ecological condition made by its developer in many North American rivers. The method is suitable only for northern temperate ecosystems, and can not be applied with confidence elsewhere, especially in ecosystems where flows are strongly seasonal. However, a modified version was developed in South Africa recently (DWAF, 1999) based on experience from local studies, and has been extensively used for planning purposes and in the scoping phase of EIA.Comprehensive methodsA range of methods exists for determination of water allocations for aquatic ecosystems which can provide answers at a higher spatial and temporal resolution than the rapid methods described above. Spatial resolution is at river reach level or smaller, temporal resolution ranges from monthly to daily flows. Application of these methods in a specific river system can take anywhere from several months to several years, since they are generally data-intensive, require detailed ecological and hydrological surveys, and usually involve multi-disciplinary teams in numerical modelling studies.Many of these methods use habitat-based endpoints: ecologists provide recommendations regarding the extent, distribution and character of available habitat which is required to maintain or protect certain ecological functions or key species, and then determine, with the help of hydrologists, the necessary magnitude, frequency, duration and timing of flows which will provide these habitats. Two aspects of habitat, viz. hydraulic and geomorphological habitat, are usually addressed in the determination process, with physico-chemical habitat sometimes being integrated into a determination. Typically, a determination involves intensive hydraulic calibration and modelling to convert the ecological parameters of water depth, wetted perimeter and velocity at key sites in the river system to the hydrological parameters of flow rate and flow volume.The best-documented examples of more comprehensive methods are the Building Block Methodology (BBM: King, Tharme & de Villiers, 2000) which was developed and has been extensively applied in South Africa, the Instream Flow Incremental Methodology (IFIM) which is widely used in the USA, and the holistic approach, which has been applied in Australia (Tharme, 1996). Recently, the new DRIFT method has been applied in the Lesotho Highlands; this is a follow-on from the BBM, developed by the same group of scientists.Once a water allocation has been determined for an ecosystem, the water must be provided at the times and rates specified. Sometimes releases are made from a dam specifically for the ecosystems downstream – measurements taken at a control point such as a flow monitoring station are used to check that the correct flows are being released, but if the dam is far upstream there may be losses of water along the way, due to evapotranspiration, evaporation, abstraction or seepage into groundwater. In other cases, if there is no dam present the water allocation for the ecosystem is used to determine how much water can be abstracted along the run of the river, and abstraction licensing conditions are set accordinglyIf the natural flow regime is to be followed as closely as possible, then flows should be released at appropriate times so as to match the natural ecological cues and signals. A flow gauging station upstream of a dam may be used to determine when a release should be made from the dam for the ecosystems downstream. After rain, if the flow into the dam begins to increase naturally, then it is time to release the flow for the ecosystems downstream of the dam to mimic natural conditions. Likewise in drought conditions, if the whole area is undergoing a natural drought, then flows for the ecosystem are reduced accordingly.Tharme R (1996). Review of international methodologies for the quantification of the instream flow requirements of rivers. Draft report to the Water Research Commission, Pretoria, South Africa.Tennant DL (1976). Instream flow regimens for fish, wildlife, recreation and related environmental resources. Fisheries 1(4): 6-10.DWAF (1999). Resource Directed Measures for Protection of Water Resources: Volume 2 Integrated Manual, Volume 3 River Ecosystems, Volume 4 Wetland Ecosystems, Volume 5 Estuarine Ecosystems, Volume 6 Groundwater Component. Department of Water Affairs and Forestry, Pretoria, South Africa.The Department of Water Affairs in South Africa published Version 1.0 of its Resource Directed Measures for Protection of Water Resources, which includes methods for determination of the water requirements of riverine ecosystems, wetland ecosystems, estuarine ecosystems and the groundwater component of these.Development of minimum water level criteria for the Everglades Protection Area.The Queensland government has published several Water Management Plans which have specific provisions for the environment.An international working conference Environmental Flows for River Systems, which incorporates the Fourth International Ecohydraulics Symposium. Cape Town, March 2002.A conference on “Managing River Flows for Biodiversity” was held in Fort Collins, Colorado, USA in July 2001. Several case studies of provision and management of river flows for aquatic ecosystems were discussed in detail. The conference agenda gives a description of each case study, and the names of contact people can be gleaned from this.This is a new section which will be added to all features, and which we would like to develop as time goes on. The aim is to provide a list of people or groups which are working in a specific field, to make it easier to establish contact with other researchers or colleagues, in government, universities, NGO sector or the private sector who might be able to collaborate or provide information. If you would like to be added to this list, please email hmackay@global.co.za, providing the website address of your group plus two to three sentences about who you are and what you do, and maybe list a couple of your key project areas. If you don’t have a website, then please provide the name and email address of the relevant contact person.AustraliaCentre for Catchment and Instream Research, Griffith University, Brisbane. Research and consultancy projects on flow requirements of instream biota.South AfricaThe Centre for Environmental Management at the University of the Free State runs a two-year, part-time coursework Masters programme in Environmental Management, which allows students to specialise in Biomonitoring and Conservation; Pollution Control and Rehabilitation; or Environmental Communication. Research by the Centre concentrates on the biomonitoring of highly seasonal and regulated rivers, including geomorphology, riparian vegetation, nutrient chemistry and algae, macroinvertebrates (SASS) and fish.”Streamflow Solutions cc.River hydraulics with particular application for assessing the environmental flow requirements of rivers and wetlands. Effect of flow regulation and management on geomorphological change within fluvial environments.Dr Drew Birkhead streamflow@icon.co.zaBotswanaNamibiaFranceMoldovaInternationalUSAMadagascarMalaysia