| 1. |
- Bragée, Petra, et al.
(författare)
-
Lake ecosystem responses to catchment disturbance and airborne pollution: an 800-year perspective in southern Sweden
- 2013
-
Ingår i: Journal of Paleolimnology. - : Springer Verlag (Germany). - 0921-2728 .- 1573-0417. ; 50:4, s. 545-560
-
Tidskriftsartikel (refereegranskat)abstract
- Sediment sequences spanning the last 800 years from two small lakes in the south Swedish uplands were explored for assessment of effects of changing human population, local land-use practices and airborne pollution on lake-ecosystem functioning and resilience. Variations in nutrient cycling and deposition of lithogenic elements were studied, using a multi-proxy stratigraphic approach. Carbon and nitrogen elemental and isotopic analyses were applied in combination with records of hydrocarbons (n-alkanes) to investigate the sources and depositional conditions of sediment organic matter. Changes in fluvial and airborne delivery of inorganic matter were based on X-ray fluorescence measurements. The results reveal that population growth and related increases in land-use pressure had a major impact on catchment erosion and input of terrestrial organic matter to the lakes from the 1500s to the end of the 1800s. Evidence also exists of a brief period of catchment disturbance at ca. 1200-1300, followed by recovery, likely connected to the Black Death pandemic. At ca. 1900 synchronous shifts in most of the proxy records suggest a marked change in external forcing common to the two lakes related to a major decrease in population density and the introduction of modern forestry following the industrial revolution. Interestingly, the two sediment records exhibit generally coherent trends in C/N ratio, organic C content and delta C-13, both before and after 1900, indicating broadly similar sensitivities of the lake ecosystems to human impact. In contrast, deviating trends in total N content, delta N-15 and lithogenic element concentrations (K, Ti, Rb and Zr) reflect site-specific responses to local disturbances during the last century due to different nutrient conditions and catchment properties. Our companion sediment records highlight the importance of understanding long-term human impact on watersheds and demonstrate how regional versus local forcing of lake ecosystems, as well as site-specific responses related to catchment characteristics can be reconstructed.
|
|
| 2. |
- Choudhary, Preetam, et al.
(författare)
-
An environmental record of changes in sedimentary organic matter from Lake Sattal in Kumaun Himalayas, India
- 2009
-
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 407:8, s. 2783-2795
-
Tidskriftsartikel (refereegranskat)abstract
- Sattal a small mountainous lake in the Kumaun Himalayas has been impacted by various cultural activities in recent years. We explored the effects of human-induced changes in this lake by using various geochemical proxies. Shifts in TOC and N flux, C/N ratio, stable isotopes (delta C-13 and delta N-15), n-alkane, and pigment concentrations in sediments indicate a steady increase in primary productivity over the last few decades. The trophic status of the lake has changed from mesotrophic to eutrophic condition. The C/N, CPI, and TAR based ratios in sediments indicate accumulation of algal matter derived primarily from in situ production, with limited input of terrestrial organic matter from the watershed. The low (between 0.1 and 1 parts per thousand) delta N-15 values imply N-2-fixation by cyanobacteria, and the decrease in delta C-13 values up-core represent the effect of sewage input and land based runoff, or possible contribution from microbial biomass. The pigments change from non-N-2 fixing cyanobacterial species to the N-2-fixing community, and are consistent with the proxy-based productivity shifts inferred in the lake. The deeper sediments are affected by post-diagenetic changes causing an increase in delta C-13 (and possibly delta N-15) due to mineralization of organic C and N.
|
|
| 3. |
- Choudhary, Preetam, et al.
(författare)
-
Biogeochemical records of paleoenvironmental changes in Nainital Lake, Kumaun Himalayas, India
- 2009
-
Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 42:4, s. 571-586
-
Tidskriftsartikel (refereegranskat)abstract
- Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns about sediment and water pollution. Lead-210 dated sediment cores from the lake represent similar to 95 years of accumulation and yield a mean sedimentation rate of similar to 4.7 mm year(-1). Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (delta C-13, delta N-15, and delta S-34), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC flux varies from 1.0 to 3.5 g m(-2) year(-1). Sediments are anoxic (Eh -328 to -187 mV) and have low (0.10-0.30 g m(-2) year(-1)) N, but high (0.37-1.0 g m(-2) year(-1)) S flux. Shifts in delta C-13, delta N-15, and delta S-34 suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the lake has remained largely unchanged, and the perceived human-induced impacts are limited.
|
|
| 4. |
- Choudhary, Preetam, et al.
(författare)
-
Distribution of polycyclic aromatic hydrocarbons in Kumaun Himalayan Lakes, northwest India
- 2010
-
Ingår i: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 41:9, s. 891-894
-
Tidskriftsartikel (refereegranskat)abstract
- Sources and historical deposition of polycyclic aromatic hydrocarbons (PAHs) were investigated in dated sediment cores from Lakes Nainital and Bhimtal in the Kumaun Himalaya The data show that PAH deposition has increased in recent years and is associated with an increase in anthropogenic activity. The lake sediments dominantly contain low molecular weight (LMW) PAHs. derived mainly from petrogenic sources Concentrations of individual and total PAHs were categorized on the basis of sediment quality criteria. According to this, the pollutants pose a potential threat to aquatic life.
|
|
| 5. |
- Choudhary, Preetam, et al.
(författare)
-
Organic geochemical record of increased productivity in Lake Naukuchiyatal, Kumaun Himalayas, India
- 2010
-
Ingår i: ENVIRONMENTAL EARTH SCIENCES. - : Springer. - 1866-6299 .- 1866-6280. ; 60:4, s. 837-843
-
Tidskriftsartikel (refereegranskat)abstract
- Organic geochemical proxies have been studied in a 45-cm-long core retrieved from Lake Naukuchiyatal in Kumaun Himalayas, India. Increase in TOC, N, hydrocarbons and pigments concentration from bottom to surface sediments of the core indicates increase in the lake productivity. Stable isotopes (δ13C and δ 15 N), biomarkers (TAR, CPI and n-ΣC15,17,19) and C/N atomic (between 9 and 12) suggest dominance of algal derived organic matter in these sediments. Decrease in organic δ13C values (between −27 and −31‰) in surface sediments indicate influence of sewage and land runoff in shifting organic δ13C values, whereas low (between −0.23 and 2.2‰) δ15N values together with high pigment concentrations (zeaxanthin and echinenone) represent dominance of cyanobacteria in the lake.
|
|
| 6. |
- Randsalu Wendrup, Linda, et al.
(författare)
-
Combining limnology and palaeolimnology to investigate recent regime shifts in a shallow, eutrophic lake
- 2014
-
Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 51:3, s. 437-448
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we demonstrate that an integrated approach, combining palaeolimnological records and limnological monitoring data, can increase our understanding of changing ecological patterns and processes in shallow lakes. We focused on recent regime shifts in shallow Lake Krankesjon, southern Sweden, including the collapse of the clear-water state in 1975 and its subsequent recovery in the late 1980s. We used diatom, hydrocarbon and biogenic silica sediment records, in concert with limnological data sets on nutrient concentrations, water clarity, chlorophyll-a and water depth, to investigate the shifts. The shift from clear to turbid conditions was abrupt and occurred over 1 to 2 years, whereas recovery of the clear-water state was more gradual, taking 4-5 years. In 1978, shortly after the first regime shift in water clarity, the diatom community underwent a significant shift. It became less diverse, with decreased abundance of epiphytic and planktonic taxa. Despite rising phosphorus concentrations and lower abundance of submerged macrophytes, Lake Krankesjon has remained in the clear-water state over the past 20 years, although this state seems to be increasingly unstable and susceptible to collapse. The complex reactions of the entire lake ecosystem to major changes in lake-water clarity, as shown by the palaeolimnological variables investigated in this study, emphasize the importance of careful lake and catchment management if a stable, clear-water state is desired.
|
|
| 7. |
- Routh, Joyanto, 1968-, et al.
(författare)
-
A sediment record of recent nutrient loading and trophic state change in Lake Norrviken, Sweden
- 2009
-
Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 42:3, s. 325-341
-
Tidskriftsartikel (refereegranskat)abstract
- Human-induced perturbations in the Lake Norrviken catchment, Sweden, over the last 100+ years have left distinctive geochemical imprints in the sediments. Disposal of sewage, industrial, and agricultural run-off into the lake since the end of the nineteenth century changed the trophic status from eutrophic to hyper-eutrophic. The primary organic matter (OM) source in the lake is in situ algal material. Total organic carbon (TOC) concentrations increased near the mid-section of a short sediment core collected from the deepest part of the lake, reflecting elevated epilimnetic productivity and consequent hypolimnetic anoxia. Accompanying shifts to lighter stable organic C and total N isotopic compositions suggest that cyanobacterial productivity increased during this period. The distribution of pigments in the core indicates a shift in the phytoplankton community to a cyanobacteria-dominated system. Moreover, pigments confirm that N-2-fixing versus non-N-2-fixing phytoplankton varied depending upon the external inputs of N and P. Conditions in the lake improved after sewage input was diverted and the lake is currently mesotrophic.
|
|
