Changes of environmental parameters due to salinity intrusion in the Southwest region of Bangladesh

Abstract

The study was undertaken to assess and identify the spatial and temporal changes of salinity with upstream river dis~harge, mean tide level and local rainfall. The main focus was to identify the enviromnenlal changes with salinity regarding fisheries and agriculture as well as development of an empirical relationship between salinity and enviromnental parameters. Two different zones such as High saline Zone and Moderate saline Zone, namely Paikgacha and Rampal, respectively, were included in the study. Infonnation was collected from two categories viz. fisheries and agriculture farmers through semi"structured questionnaire regarding the change.' "f environmental parameters due to salinity over the 30 years period from 1975-2005. Some useful indices of species stmcture in communitie" and conventional statistical techniques were used, TIle srndy has revealed that in Paikgacha, the salinity varies within the rilllge from 20,000 to 45,000 micro-mhos and in Rampal it is from 10,000 to 30,000 micro-mhos, It has shown that a limited degree positive and negative relationship e~ists between salinity and river discharge, and mean tidal water level and local rainfall but those relationships are significant slatistical1y. 1lhas been found that rainfall and river discharge arc the key factors to control salinity for Paikgacha and Rampal respectively. Salinity intrusion ha, caused SeVerethreat to the fresh water fish diversity. The species in Palkgacha and Rampal have heen reduced from 29 to 12 and 24 to 18 respectively during lile perIod 1975-2005. Species diversity, richness and evelllless have been decreasing in both areas but it is more visible in Paikgacha. Fish divcrsity (Hi, richness (d) and eVeIIllCSS(e) have been reduced III Paikgacha from 3.272 to 2.409, 6.956 to 3.376 and 0.972 to 0.969 respectively during the smdy period. Whereag, in Rampal, H', d, and e have been ",duced frOIll 3.148 to 2,844, 5,51 to 4.82an<J 0,991 to 0.984 respectiveiy. Dominancy of saline tolerant species has also increased in both region, hut severe in Paikgacha, Presently the farmers of these areas are more interested in slmmp and carps. Hahitatloss is also the cause of dIversity loss. Small land holders are sellinglleasing their lands to shrimp cultivators that results in the change of ownership pattern in hoth areas. Due to salinity intrusion, indigenous ri,e varieties have been reduced by 75% in Paikgacha and 33.33% in Rampal during the period 1975-2005, Rice yield has been decreased by 67.30% and 69.70% in Rampal and Paikgaeha respectively during the srndy period. Rabi vegetable has been affected more than klwrif vegetable. \( results in lowering the diversity inde~ value of Paikgaeha and Rampal from 2,766 to 0.694 and 2,685 to 2.349 respectively during the study period, Saline intolerant spccics have been departing and saline tolerant species like babla, khejur, etc are dominating In both regions due to salinity. It has reduced plant diversity inde~ valuc from3,397to 2.530 in Paikgacha and 3.537 to 2.931 m Rampal during thc pcrlod 1975-2005. There is no remarkable change in cropping pattern ami intensity in both regions. Most of the people of these two areas are more interested in rice Cumfish fanning but in Rampal, people are also ulterested in rIce cum fish and freshwater f"h cullure. No empirical, semi-empirical Of analytical equation e~ists to compute the change of enviromnental parameters as a result of change of physical parameters like salmity. In this regard, an altempt was ntade to develop an empirical equati(ln. The equation was developed for Paikgacha but il not generally applicable to other areas.