The Sources of Carbon and Nitrogen in Mountain Lakes and the Role of Human Activity in Their Modification Determined by Tracking Stable Isotope Composition

Abstract

We studied the isotopic composition of organic matter in the sediments of eight mountain lakes located in the Tatra Mountains (Western Carpathians, Poland). The sediments of the lakes were fine and course detritus gyttja, mud, and sand. The total organic carbon content varied from 0.5 to 53 %. The C/N ratio indicated that in-lake primary production is the major source of the organic matter in the lakes located above the treeline, whereas terrestrial plant fragments are the major organic compounds in the sediments of dystrophic forest lakes. We also found that a clear trend of isotopic curves toward lower values of δ13C and δ15N (both ~3 ‰) began in the 1960s. This trend is a sign of the deposition of greater amounts of NOx from the combustion of fossil fuels, mainly by vehicle engines. The combustion of fossil fuels in electric plants and other factories had a smaller influence on the isotopic composition. This trend has been weaker since the 1990s. Animal and human wastes from pastures and tourism had a surprisingly minor effect on lake environments. These data are contrary to previous data regarding lake biota and suggest the high sensitivity of living organisms to organic pollution.

Recent changes in production in oligotrophic Uinta Mountain lakes, Utah, identified using paleolimnology

“…Fish stocking is expected to cause an increase in d 15 N (Gasiorowski and Sienkiewicz 2013). Organic matter d 15 N typically increases by , 3%-4% with each trophic level of the lake food web (Minagawa and Eitaro 1984), so the repeated introduction of fish to these lakes over the last 50 yr should result in 15 N enrichment of the lakes (Gasiorowski and Sienkiewicz 2013). Fish undernourishment, as has been reported in Bluebell Pass Lake (Rabe 1968) andNo Name andEast Carrol Lakes (Utah Division of Wildlife Resources 1978 unpubl.…”

The effect of fish stocking on mountain lake plankton communities identified using palaeobiological analyses of bottom sediment cores

“…Wielki Staw Polski is located a few metres lower than PSP, so during high water levels (e.g., spring melting), the lake can be supplied by the water from PSP and other surrounding ponds. The isotopic composition of the sediments of Wielki Staw Polski may be indirectly linked to processes taking place in Przedni Staw Polski (Gąsiorowski and Sienkiewicz 2013). As a result of intensive tourism, there is an increase in soil erosion around the lake, which delivers allogenic material with nutrient loads from the catchment (Toro and Granados 2002).…”

“…Assessment of the effect of fish introduction on primary fishless lakes in the Tatra Mountains cannot be based solely on the direct interpretation of the subfossil record. Despite their remote location, the lakes in the Tatra Mountains have been affected by global and regional climatic and environmental changes, including intensive tourism and acid deposition (Gąsiorowski and Sienkiewicz 2013;Sienkiewicz and Gąsiorowski 2014). These global and regional effects have interfered with the local impact of fish stocking.…”

Can fish introductions alter nutrient cycles in previously fishless high-latitude lakes?

“…Taking into account the pigment trends and the accumulation rates of diatoms (Weckström, unpublished data), which do not show any significant trend, it is unlikely that a production increase has actually occurred. Previous studies noted that δ 15 N ratios should increase 3-4‰ in lakes where fish populations have cascading effects on phytoplankton production, as increased phytoplankton biomass usually produces higher values of δ 15 N due to a preferential utilization of 15 N (Gąsiorowski and Sienkiewicz, 2013). Furthermore, increased phytoplankton biomass often decreases δ 13 C ratios in sediments, due to the preferential utilization of 12 C (France, 1995).…”

“…Fish predation can move and transform nutrients derived from benthic or terrestrial prey to a bioavailable excretion in the pelagic areas of lakes, resulting in a net regeneration of nutrients. However, isolating the effects of fish introductions on the trophic state of lakes from other concurrent pressures remains challenging (Gąsiorowski and Sienkiewicz, 2013).…”