JSARD: ISSN 1811-8976, Volume 8 Issue 3 2010 794 J. Subtrop. Agric. Res. Dev. 8(3): 794-799, June 2010 website: www.gscience.net or www.gurpukur.com A BIO-PHYSICAL RELATIONSHIP: BIODIVERSITY WITH SALINITY MD. NAZIM UDDIN 1 *, ANISUL HAQUE 2 and MD. SALEQUZZAMAN 1 ABSTRACT Environmental parameters change due to salinity regarding agriculture and fisheries ecosystem as well as development of an empirical relationship between salinity and diversity has been studied in 2005. Two different zones in southwest coastal region of Bangladesh such as high saline zone Paikgacha upazila under Khulna district and moderate saline zone Rampal under Bagerhat district in Bangladesh have been considered as study area. Information was collected from agriculture and fisheries farmers through semi-structured questionnaire regarding agro-fisheries changes due to salinity over a period of 30 years from 1975-2005. Some useful indices of species structure in communities and conventional statistical techniques were used. Due to salinity intrusion, indigenous rice varieties have been reduced by 75% in Paikgacha and 33% in Rampal. Crop diversity index value of Paikgacha and Rampal has been reduced from 2.77 to 0.69 and 2.69 to 2.34 respectively. Saline intolerant species have been departing and saline tolerant species are dominating in both regions. It has reduced plant diversity index value from 3.40 to 2.53 in Paikgacha and 3.53 to 2.93 in Rampal. The fish species in Paikgacha and Rampal have been reduced from 29 to 12 and 24 to 18 respectively. Fish diversity (H - ), richness (d) and evenness (e) have been reduced in Paikgacha from 3.272 to 2.409, 6.956 to 3.376 and 0.972 to 0.969 respectively, whereas, in Rampal, all these (H - , d and e) have been reduced from 3.148 to 2.844, 5.51 to 4.82 and 0.991 to 0.984 respectively. Dominancy of saline tolerant species has also increased in both regions but more in Paikgacha. An attempt was made to develop an empirical equation to compute the change of environmental parameters as a result of change of physical parameters like salinity. The equation was developed for Paikgacha but is not generally applicable to other areas due to its limitation. Keywords: Salinity, Agriculture, Fisheries, Diversity, Empirical equation and Southwest region. INTRODUCTION The land area of Bangladesh coastal zone is 42,154 sq. km. covering all 16 sea and estuary-facing administrative districts. It occupies 19.1% irrigated area of the total land area (PDO-ICZMP, 2001). The environmental and economic significance of the coastal zone to the country is undeniable. More than 30% of the net cultivable area is in the coast and some of the best agricultural land lies here (Bhuiyan, et al., 1998). Coastal area has tremendous potential for agriculture and aquaculture development. This is particularly important because of the adverse man-land ratio in Bangladesh but salinity problem has changed the farming system of this region. A significant change is taking place in environmental parameters such as agro-fisheries ecosystem because of salinity intrusion (Ahmed, 2002). The successive salinity increment has a direct impact on environmental sustainability. The changes to ecosystems are multilateral. About 20% of the net cultivable land of Bangladesh coastal region is affected by different degrees of salinity (Karim et al., 1990). Along with other factors shrimp cultivation plays a major role to increase soil salinity particularly in southwestern coastal areas (SRDI, 2003). Soil salinity is the most dominant limiting factor towards crop growth in the coastal belt especially during the dry season. Salinity causes unfavorable environment and hydrological situation restricting the normal crop production throughout the year. This reduces the crop area and restricts the cultivation of aus (summer rice), boro (dry season rice) and other rabi (dry season) crops (Islam and Ahmad, 2004). Local crop diversities are disappearing and cropping pattern has been changed (Tutu, 2004). Flow reduction in this particular region has severely affected the historical river regime that allowed the intrusion of the saline front leading to severe dislocation of the life cycle of the fish population. This affected the spawning ground leading to substantial reductions in the inland open water fishery (Rabbi and Ahmed, 1997). Various fish species can not get feasible environment in this region for reproduction (Ali, 1999). As a result, fish diversity with fish habitat has been changed. Salinity intrusion is one of the most important physical phenomena in estuaries that affect the quality of both surface and ground water. In addition, salinity is the major environmental factor influencing the biodiversity in brackish water (Remane and Schlieper, 1971) and its variation determines the diversity of species in estuaries (Attrill, 2002; Etemad et al., 2008). 1 Environmental Science Discipline, Khulna University, Khulna-9208, Bangladesh, 2 Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh. *Corresponding author’s Email: naz_es@yahoo.com