Determining whether an 18/16O technology threshold exists in estimating lake primary productivity and associated metabolism

Abstract

To determine lake carbon (C) cycling storage, transport, and transformation functions, it is necessary to understand metabolic lacustrine changes and associated drivers, all of which are premised on accurate metabolic estimates. The continuous improvement in conventional metabolic lake methods and the emergence of novel relevant methods in recent years have led to confusion as to their usage. Although 18/16O technology has recently been more widely used, its applicability remains controversial among researchers. The Qinghai–Tibet Plateau (QTP) is an exceptional location for such experimental studies, primarily due to its many different natural lake types. This study used 18/16O technology to investigate 19 lakes of different salinity (0.0 ∼ 196.0 ‰), area (5.0 ∼ 4345.9 km2), and altitude grades (2549.9 ∼ 4541.8 m) on the QTP to determine their specific metabolism. Results show that 18/16O technology is not suitable for use for high saline and low dissolved oxygen lakes (i.e., a salinity level greater than 35‰ and a dissolved oxygen level < 4 mg L-1). Under low dissolved oxygen conditions caused by high salinity, alterations in isotopic fractionation will cause 18/16O technology to fail. These findings can be used as a reference for estimating lake metabolism as well as researching nutrient cycling while also promoting metabolic estimation method improvements.