Agricultural development and impacts on wetlands : trade-offs for waterbird conservation in Sri Lanka

• Main Author: Bellio, Maria Grazia
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: UNSW Sydney 2011
• Subjects: Wetlands; Waterbirds; Agriculture; Ecosystem services; Biodiversity; Functional ecology; Shorebirds; Pacific; black-tailed godwit; Copepods
• Online Access: https://dx.doi.org/10.26190/unsworks/23750; http://hdl.handle.net/1959.4/50944

There is a real urgency for waterbird conservation action in the Asia-Pacific region where currently 71% of waterbird populations are declining. Waterbirds depend on wetlands for most of their life cycle. Agricultural intensification and unsustainable use of water resources are the most important threat to wetland habitats. Agricultural development and wetland conservation have often been portrayed as direct trade-offs between human need for food versus conservation, however there is increasing global understanding that human well being and environmental sustainability are intrinsically interconnected. Wetlands provide important ecosystem services and so loss of biodiversity affects human well being as well as ecosystem health. I focused my research in the Asian developing country of Sri Lanka and investigated the interaction of human water use for agriculture and waterbird ecology on a system of natural coastal brackish lagoons (one of the three more important Ramsar sites) potentially degraded by recent expansion and development of agriculture. Freshwater artificial (human-made) wetlands (salt evaporation ponds, irrigation reservoirs and rice paddies) were upstream of the Ramsar site within the agricultural area, affecting the coastal lagoons hydrology. I had two main core research questions on potential loss of waterbird biodiversity and its relationship on ecosystem function for the wetlands in my study area. The first was to determine whether natural wetland ecosystems affected by anthropogenic impacts can maintain functional properties and processes comparable to non impacted systems. The second was to find out whether artificial wetland systems can function as surrogates for degraded or destroyed natural wetland systems. I investigated five components of waterbirds biodiversity relating to wetland functionality (species richness, evenness among species, species composition, functional group richness and composition) and compared the waterbird communities of natural and artificial wetlands. Direct manipulative experiments on waterbird biodiversity and ecosystem processes were not possible and so I measured environmental variables: water levels and water quality, habitat characteristics (vegetation structure and complexity) and food resources to identify relationships between components of waterbird biodiversity and ecosystem function. Agricultural development had detrimentally altered the ecological character and functionality of one the coastal lagoons of the Ramsar site. Impacts included hydrological disruption of natural cycles of flooding and drying, increased water turbidity and decreased salinity levels. These impacts were directly reflected in the abundance and composition of the waterbird communities of the impacted lagoon that had become ecologically similar to freshwater artificial wetlands. As with freshwater artificial wetlands, resident waterbird species (waterfowl and egrets and herons) were more abundant than long distant migratory shorebirds on the impacted lagoon. Disruption of the hydrological cycle had reduced temporal availability of suitable shorebird foraging areas (shallow areas <30cm) as well as abundance and composition of their food resources. Lack of hydrological variability and waterlogged habitats had favoured abundance of planktonic prey (copepods) and aquatic insects versus benthic prey on the impacted lagoon. Availability and abundance of benthic prey (amphipods, prawns, ostracods, and molluscs) directly affected the foraging efficiency of many long distant migratory species (black-tailed godwit, curlew sandpiper, lesser sand plover, little stint) that depend on these prey. On the impacted lagoon, foraging efficiency of some shorebird species was affected by water levels rather than prey abundance: high water levels constrained the foraging of species that fed by walking (black winged stilt), while turbidity reduced visibility for visual foragers (lesser sand plover, Kentish plover). Maintenance of the ecological character of the Ramsar site will depend upon re-establishment on the impacted lagoon of pre-development conditions (natural hydrological cycle, water chemical parameters), and restoration of the natural wetland's functionality. Quality of habitat and food resources on artificial wetlands located upstream the RAMSAR site were not functionally ecologically equivalent to the natural coastal wetlands. Imposed hydrological stability on artificial wetlands affected vegetation structure and shoreline complexity. Reduction in habitat complexity affected waterbird biodiversity, in particular abundance of shorebird species. Waterbird food resources were less abundant on artificial than on natural wetlands. Human disturbance and mechanisms of interference competition also affected waterbird foraging efficiency on artificial wetlands. Currently long term conservation of waterbirds, and in particular migratory shorebird species, in the study area will depend on the maintenance of healthy functional natural wetlands. This will include improving habitat quality and functionality on artificial wetlands. Opportunities exist to manage artificial wetlands to improve current habitat (improve hydrological variability and vegetation complexity) condition for waterbirds and their food resources (limitation of use of pesticides in rice paddies). These management practices may as well benefit many other ecosystem services (fisheries, tourism, water for livestock, cultural-religious activities) these wetlands provide to people. The study demonstrated the importance of the system for waterbirds but also the effects of different human pressures on its functionality. Artificial wetlands established primarily to service the irrigation industry failed to have sufficient functionality and were not suitable replacements for natural wetlands. Further, the altered hydrological regime on one of the Ramsar wetlands, used as a drainage area for surplus irrigation water, was detrimental to its functionality. Much of this understanding about ecosystem function and interaction was established by using waterbirds as a useful proxy. Separating species into different guilds and then examining patterns of abundance and distribution shed considerable light on the different interactions that underpinned the ecology of coastal lagoons and artificial wetlands in Sri Lanka.