|Inland Waters Biodiversity: Overview|
Inland water biodiversity is defined simply as biodiversity associated with the inland water ecosystem. Water as a physical resource is not biodiversity but the life associated with it is. Water and inland biodiversity issues cannot be separated. Inland water biodiversity is critically important to human well-being. They provide food security and livelihood through fisheries and other resources, and also support many ecosystem services such as climate regulation, flood mitigation, nutrient cycling, groundwater recharge, water purification and waste treatment.
The Bureau of Fisheries and Aquatic Resources or BFAR (1995) defined inland water resources in the country to include swamplands (fresh and brackish), fishponds (fresh and brackish) and other inland resources (lakes, rivers, reservoirs).
The NBSAP listed 78 lakes (DENR, 1977) while the Philippine Biodiversity Conservation Priorities (PBCP) included 211 lakes varying from .01 sq km to 900 sq km, 18 major rivers and 22 marshes, swamps and reservoirs (Ong et al, 2002). There are 10 major lakes that host aquaculture production and many other uses such as for household, recreation, and industry. There are also 421 principal river basins that provide various services for households, transportation, irrigation, and many others. These rivers drain in areas ranging from 41 sq km to 25, 649 sq km, with about 20 of them considered as priority river basins. (DENR-RBCO, 2007). Lakes and rivers occupy 1,830 sq km or 0.61 percent of the total inland water area. The PBCP prioritized 34 inland water bodies for research and conservation.
Inland waters are home to a more than 316 fish species, some of which are endemic and confined to single lakes such as the Sardinella tawilis found only in Taal Lake. Fishbase records as of 2008 show that there are about 121 endemic and 76 threatened freshwater species. Other than fish, other species that depend on these habitats are waterbirds, semi-aquatic species like the highly endangered Philippine crocodile (Crocodylus mindorensis), plants, and a majority of amphibians.
Unfortunately, inland waters are also the most threatened of all ecosystem types. Globally, the main threats are: physical alteration, habitat degradation, water withdrawal, overexploitation, pollution, and introduction of invasive alien species. In the Philippines, Ong et al, 2002 and the Environmental Management Bureau or EMB (2006) identified pollution from domestic (33%), industrial (27%), agricultural (29%) and non-point sources (11%) as the major reason for biodiversity loss in inland waters. Because of pollution, water quality decreases causing heavy algal blooms and oxygen depletion. Other threats include habitat loss and degradation; (b) resource use and exploitation; (c) climate change; and, (d) alien invasive species. Introduction of invasive alien species has also caused near-extinction of local endemic species. Diversion of rivers for irrigation and dam construction has also affected movement of migratory fish species, changed the habitat of riverine flora and fauna, and dried rivers. Population pressure remains one of the biggest threats.
For this Report, discussion on status, trends and threats is limited to some inland water bodies where sufficient information is available. As in the other ecosystems, there has been difficulty in determining status, trends and threats at the national level due to lack of data, lack of monitoring systems, and lack of capacity among institutions. This Report also used water quality indicators such as levels of dissolved oxygen (DO) and biological oxygen demand (BOD) primarily because historical data is available. DO is defined as the amount of oxygen available in the water for fish and other aquatic organisms to live. An average DO level of less than 5mg/L may be detrimental to fish and other aquatic communities, so the higher the DO level, the better the water quality, the better for biodiversity. BOD is defined as the amount of oxygen used by microorganisms to decompose organic matter. An average BOD level of not more than 7 mg/L is good for fishery. The lower the BOD level, the better the water quality, the better for biodiversity. The DENR-EMB has classified 525 water bodies in terms of best usage and water quality in about 263 principal rivers, 213 minor rivers, 7 lakes, and 42 coastal and marine waters, representing about 62.5% of the water bodies in the country Table 8 shows the classification and number of water bodies in 2005 and 2006 (EMB, 2006 and 2007).