ABSTRACT: Because the Truckee River link togethers two lakes along the Eastern Sierra Nevada Mountains with different limiting nutrients.

ABSTRACT:

Because the Truckee River link togethers two lakes along the Eastern Sierra Nevada Mountains with different limiting nutrients, this research addresses whether the nitrogen:phosphorus (N:P) balance of the river ecosystem changes longitudinally. Historical (1990 to 2000) total nitrogen:total phosphorus (TN:TP) ratios in river water exhibited the wait fored gradient from high N:P ratios upstream to cheap N:P ratios downstream, with the major gradient of the N:P balance occurring within the transition between montane and high untilled terrain. During 2001, the river contained anomalously reasonable total nitrogen concentrations in the far upper reaches and dissolved inorganic nitrogen concentrations in the lower reaches, resulting in a les apparent longitudinal gradient of N:P ratios. Measurements of periphyton expansion and physiology (nutrient bioassays and ectoenzyme activities) and stoichiometry during the summer of 2001 also exhibited a web picture of the spatial variation of N:P balance that was not entirely consistent with a able to endure N:P gradient. However, the compendium of the indicators did support the overall picture of an overarching longitudinal gradient from high to reasonable N:P ratios. The results insinuate that periphyton management efforts in the Truckee River should consider the overall spatial gradient as well as the small-scale dynamics of the stream ecosystem texture

(KEY TERMS: periphyton; nutrient limitation; algae; aquatic ecology; nutrients; water quality.)

INTRODUCTION

In loticecosystems, periphyton (photosynthetic assemblages that attach to substrates) are a substantial element of the total autotrophic biomass, and as primary farmers periphyton are integral to providing manliness to stream food webs (Allan, 1995) However, excessive periphyton expansion can impair ecosystem health. For instance, reasonable dissolved oxygen concentrations in lotie ecosystem are frequently due to autotrophic respiration (eg Carlton and Wetzel, 1987; Zagorc-Koncan et al., 1991; Allan, 1995) and can be harmful to fish survival (Brung 1971) Degradation of ecosystem health according to excessive periphyton growth can ultimately ensue in the loss of ecosystem diversity as well as a los in aesthetic and recreational quality of a river or stream (see Chapra, 1997; Biggs, 2000)

Relationships exist between periphyton abundance and nutrient concentrations in many lotie ecosystem (eg Dodds et ai, 1997; Biggs, 2000) and nutrients are frequently a limiting resource for periphyton shooting (Borchardt, 1996). Thus, effective management of periphyton in lotie ecosystem requires an understanding of nutrient limitation in the arrangement being managed - whether nutrient limitation exists and if in the way that what nutrient(s) are limiting. If the existence of nutrient limitation has been established and the nutrient limiting periphyton germination has been identified, management for the limiting nutrients can increase the effectiveness of periphyton management. However, nutrient limitation in lotie ecosystem is not static. Nutrient limitation has been shown to change temporally (eg Francoeur et al., 1999; Rosemond et al., 2000) and is awaited to change spatially (see Biggs et al., 1998; indentation and Grimm, 1999). Thus, vigorous management of periphyton requires an understanding of the temporal and spatial variability of nutrient limitation.

Longitudinal (upstream to downstream) changes in N and P concentrations in rivers have been documented (Mulholland and Rosemond 1992) Ratios of N:P invest have been cited as evidence of longitudinal changes between N and P limitation of periphyton sprouting in streams of New Zealand (Biggs et al., 1998) and Arizona (Dent and Grimm, 1999) Wold and Hershey (1999) showed that adjacent watersheds along the North Shore of Lake Superior had different nutrients limiting periphyton vegetation but no switch between N and P limitation within a watershed was apparent. Considering these studies, it might be calculate uponed that spatial variation of nutrient limitation exists within lotie ecosystem if it were not that has yet to be thoroughly examined.

Both P limitation (eg Bothwell, 1985; Allan, 1995) and N limitation (eg Grimm and Fisher, 1986; Leland, 1995) have been demonstrated to flash on the mind in lotie ecosystems of western North America. The mountainous topography of the region creates watersheds with headwaters at to a great degree higher elevations than their terminus. The elevation difference in one watersheds creates significant variation of precipitation within the watersheds (eg Barros and Lettenmaier, 1993; Basist et al., 1994) Meso scale variation of climate (hundred of kilometers) and changes in watershed gradient accommodate geomorphic, hydrologic, and botanic variation within a watershed. Spatial changes of nutrient resource limitation are more likely to come into one's head in a watershed with significant spatial variation than in a watershed with more uniformly distributed hydrology geomorphology, and botany.

Previous nutrient limitation studies in the Truckee River watershed have focused onward Lake Tahoe and Pyramid Lake. Phytoplankton in Lake Tahoe changed from N-limited to P-limited growing during the 1980s (Goldman et al., 1993) Phytoplankton in Pyramid Lake are consistently N-limited (Lebo et al., 1994) Because the Truckee River unites these two lakes with different balances of N and P this work addresses the hypothesis that the river water N:P balance changes from high N:P ratios upstream to subdued N:P ratios downstream and that periphyton physiology would spatially vary in replication to the N:P gradient. Thus, the objective of this research was to assess the longitudinal N:P balance of the Truckee River and to evaluate the drifts of any changes in the N and P abundances upon periphyton growth and nutrient biogeochemistry. If a change from a high N:P environment to a reasonable N:P environment occurs, the inferences to lotie ecosystem function and water management practices must be considered.