Contribution to high altitude limnology of the Himalayan system I. Limnology and primary productivity of the plankton community of Nilnag Lake, Kashmir

Abstract

The Nilnag (alt. 2180 m) situated in the Kashmir Himalayas, marks the beginning of the dimictic lake series of this region. The high turbidity of water (ηt : % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\] = 1.16) as a result of accelerated particle movement from the adjoining terrestrial ecosystem, has affected the sensitive macroflora which was recorded five decades ago. The lake water chemistry depicts a cation pattern which is dominated by divalent calcium (Ca⁺⁺ > Mg⁺⁺ > Na⁺ > K⁺) and the anions by a carbonate-bicarbonate system (HC′O₃ > SO″₄ > Cl′). The ionic composition of the lake water comes close to the World Standard for freshwater lakes. The levels of ortho-phosphate and nitrate-nitrogen are not very high, indicating ‘moderate fertility’ of the lake. The phytoplankton production, as measured by ¹⁴C isotope technique, ranged from 120–562 Σ mgC_assim m⁻² d⁻¹ during the ice-free period (1975–76) with an annual estimated yield of 90–100 gC m⁻². The vertical distribution of production is suggestive of plankton rich lake water. In its general limnological features, the Nilnag resembles mesotrophic lakes of the Kashmir valley.