Long-term declines in phosphorus export from forested catchments in south-central Ontario

2009 ◽  
Vol 66 (10) ◽  
pp. 1682-1692 ◽  
Author(s):  
M. Catherine Eimers ◽  
Shaun A. Watmough ◽  
Andrew M. Paterson ◽  
Peter J. Dillon ◽  
Huaxia Yao
Keyword(s):  
Stream Flow ◽  
Seasonal Patterns ◽  
Forested Catchments ◽  
Annual Average ◽  
Temporal And Spatial Patterns ◽  
South Central ◽  
Hydrologic Event ◽  
Temporal And Spatial ◽  
Shield Lakes

Total phosphorus (TP) levels in many Canadian Shield lakes in central Ontario have declined over recent decades, despite increases in human activity in most watersheds. To investigate the contribution of changes in catchment export to long-term declines in lake TP, we examined temporal and spatial patterns in TP concentrations and export (1980–1981 to 2001–2002) across 11 subcatchments that drain into three lakes in which average ice-free TP levels have declined by approximately 35%. Annual stream export of TP decreased significantly by 30%–89% in eight of the 11 subcatchments, and decreases in export were driven by declines in TP concentration, not changes in stream flow. Annual average TP concentrations varied fivefold among adjacent subcatchments, and temporal patterns in annual average TP concentrations were poorly correlated. Seasonal patterns of TP concentration were most similar among streams in the spring (March–April–May), and TP export in the spring declined significantly in 10 of the 11 subcatchments. Because spring melt is the principal hydrologic event in these seasonally snow-covered basins, decreases in TP export during the spring were primarily responsible for declines observed in annual export. The drivers of changes in TP over time are unclear at this point but are the focus of current research.

A comparison of pre-industrial and present-day changes in Bosmina and Daphnia size structure from soft-water Ontario lakes

2010 ◽  
Vol 67 (4) ◽  
pp. 754-762 ◽  
Author(s):  
Jennifer B. Korosi ◽  
Andrew M. Paterson ◽  
Anna M. DeSellas ◽  
John P. Smol
Keyword(s):  
Body Size ◽  
Size Structure ◽  
South Central ◽  
Zooplankton Size ◽  
Copepod Predation ◽  
Post Impact ◽  
North Temperate Lakes ◽  
Impact Data ◽  
Shield Lakes

Understanding the long-term controls on cladoceran size structure has important implications for aquatic ecosystems. Although there has been considerable interest in zooplankton size trends for Canadian Shield lakes, data are not available for zooplankton size structure prior to the period of anthropogenic disturbances. Here, we present pre- and post-impact size data for the common pelagic cladocerans Bosmina and Daphnia for 44 well-studied Shield lakes in south-central Ontario (Canada). We show that Daphnia were larger and that the length of Bosmina body appendages (mucrones and antennules) was longer in pre-industrial times than they are today. The reduction in Bosmina appendage length we observed may suggest a reduction in copepod predation pressure since pre-industrial times. Reduced maximum body size in Daphnia is a predicted response to a warming climate in north temperate lakes; however, we suggest that alternate explanations, specifically acidification and subsequent recovery following emission reductions, should also be explored as the primary drivers of Daphnia size changes in this lake set. Overall, our results highlight the importance of pre-impact data for understanding the long-term controls on cladoceran body size from pre-1850 to present.

Interannual variability and species turnover of crustacean zooplankton in Shield lakes

1999 ◽  
Vol 56 (1) ◽  
pp. 162-172 ◽  
Author(s):  
Shelley E Arnott ◽  
Norman D Yan ◽  
John J Magnuson ◽  
Thomas M Frost
Keyword(s):  
Sampling Error ◽  
Species Turnover ◽  
Crustacean Zooplankton ◽  
Annual Data ◽  
Turnover Rates ◽  
High Turnover ◽  
South Central ◽  
Census Interval ◽  
Shield Lakes

We estimated apparent species turnover rates and richness of the zooplankton annually over a 12-year period in eight lakes in south-central Ontario. Although species richness varied little among years (CV = 13%), apparent species turnover rates averaged 16%/year. This apparent turnover varied among years and was influenced by census interval, the number of censuses, the occurrence of rare species, and lake pH. However, Monte Carlo simulations indicated that turnover attributable to sampling error was high. That is, despite high apparent turnover rates, we cannot be certain whether interannual changes in community composition result from immigration and extinction of species because sampling error could largely account for all apparent turnover. Regardless of the source of apparent turnover (sampling or immigrations and extinctions), high turnover rates imply that zooplankton biodiversity can be underestimated in short-term studies because we detect a different assemblage of species every year. Only one third of the total species pool for each lake was detected every year. Annual data underestimated long-term species pools by 33-50%.

Quantitative inferences of past hypolimnetic anoxia in south-central Ontario lakes using fossil midges (Diptera: Chironomidae)

1998 ◽  
Vol 55 (3) ◽  
pp. 587-596 ◽  
Author(s):  
Roberto Quinlan ◽  
John P Smol ◽  
Roland I Hall
Keyword(s):  
Weighted Averaging ◽  
Species Variation ◽  
Calibration Model ◽  
Forward Selection ◽  
Lake Ecosystems ◽  
South Central ◽  
Hypolimnetic Oxygen ◽  
Chironomid Assemblages ◽  
Shield Lakes

The ability to infer long-term changes in hypolimnetic oxygen levels is important for ecological studies of eutrophication and the impacts of climatic change on freshwater lakes. We examined the distributions of fossil midge (Diptera: Chironomidae) assemblages in the surface sediments of 54 south-central Ontario lakes and, using canonical correspondence analysis (CCA), determined if fossil chironomid assemblages could be used to reconstruct levels of hypolimnetic anoxia in thermally stratifying Laurentian Shield lakes. Anoxia was expressed as the anoxic factor (AF), which represents the days per season that a sediment area equal to a lake's surface area is overlain by anoxic water. Forward selection in CCA showed that AF, maximum depth, [SO4], [Na], and watershed area all explained significant portions of species variation. A weighted-averaging regression and calibration model of the chironomid-anoxia relationship was developed which suggests that it is possible to infer AF from fossil chironomid assemblages ( (r2appar ) = 0.70, bootstrapped RMSE = 6.5 days/summer). Quantitative reconstruction of past changes in anoxia using fossil Chironomidae should provide a new and useful tool for paleoecological assessments of lake ecosystems.

Long-term trends in hypolimnetic volumes and dissolved oxygen concentrations in Boreal Shield lakes of south-central Ontario, Canada

2019 ◽  
Vol 76 (12) ◽  
pp. 2315-2325 ◽  
Author(s):  
Clare Nelligan ◽  
Adam Jeziorski ◽  
Kathleen M. Rühland ◽  
Andrew M. Paterson ◽  
John P. Smol
Keyword(s):  
Dissolved Oxygen ◽  
Climatic Factors ◽  
Thermocline Depth ◽  
South Central ◽  
Air Temperatures ◽  
Hypolimnetic Oxygen ◽  
Long Term Trends ◽  
Shield Lakes ◽  
Carbon Concentrations

Temperature–oxygen profiles, collected biweekly to monthly for ∼40 years, were used to calculate end-of-summer volume-weighted hypolimnetic oxygen (VWHO) concentrations in six small lakes located in south-central Ontario, Canada. Coherent decreases in thermocline depth and increases in hypolimnetic volume, mean hypolimnetic dissolved oxygen (DO) concentration, and VWHO were observed in five of the six study lakes. All lakes underwent an abrupt increase in VWHO and mean hypolimnetic DO after 2010. In four of the six study lakes, the highest hypolimnetic DO concentrations were observed in years where chlorophyll a concentrations were low, whereas at five of the six study lakes the highest hypolimnetic volumes were observed when dissolved organic carbon concentrations were relatively high. Warmer spring or winter air temperatures were associated with higher hypolimnetic DO concentrations at two sites, and longer ice-free periods were associated with smaller hypolimnetic volumes at two sites. These results suggest that the recent VWHO increases in the studied south-central Ontario lakes may be a function of multiple drivers that include changes in primary production, lake water transparency, and regional climatic factors.

Temporal and spatial patterns of salinity in a catchment of the central wheatbelt of Western Australia

Soil Research ◽  
2010 ◽  
Vol 48 (4) ◽  
pp. 326 ◽  
Author(s):  
M. J. Robertson ◽  
R. J. George ◽  
M. H. O'Connor ◽  
W. Dawes ◽  
Y. M. Oliver ◽  
...  
Keyword(s):  
Spatial Patterns ◽  
Western Australia ◽  
Native Vegetation ◽  
Base Line ◽  
Catchment Scale ◽  
Management Options ◽  
Temporal And Spatial Patterns ◽  
Temporal And Spatial ◽  
Saline Land

Many estimates have been made of the future likely extent of salinity at regional and national scales in Australia; however, there are few detailed studies of changes in temporal and spatial patterns at catchment scale. This study was conducted in the Wallatin and O’Brien catchments in the low–medium rainfall zone of the central wheatbelt of Western Australia, where we examined the spatial trends in saline land over the last 18 years and related these to the likely rate and extent of future salinisation. The analysis showed that: (1) salinity has continued to expand post-1999 in landscape positions where there has been watertable rise and also in areas now at equilibrium even though rainfall has been below average; (2) increases in the area of salinity are still dominated by increases in the valley floor but there is now the emergence of many small, isolated outbreaks on the adjacent slopes; (3) widely available satellite-derived salinity maps (LandMonitor) derived in 1998 provide a reliable base-line for saline mapping but now underestimate the area of salt-affected land by 60%; (4) the trend in watertable levels and time since clearing and interactions with proximity to uncleared native vegetation provide reliable predictors of salinity risk; (5) episodic rainfall in areas of shallow watertables is proposed as a significant cause of the expansion in observed salinisation, even though some of this may be transient. These results are discussed in terms of management options for farmers and the likely long-term outlook for expansion of salinity in the catchment.

Long‐term temporal and spatial patterns in bioeroding sponge distribution at the Abrolhos Bank, Brazil, Southwestern Atlantic

2019 ◽  
Vol 40 (3) ◽  
Author(s):  
Fernando Coreixas Moraes ◽  
Fernanda Cervi ◽  
Cláudia S. Karez ◽  
Leonardo T. Salgado ◽  
Rodrigo L. Moura ◽  
...  
Keyword(s):  
Spatial Patterns ◽  
Southwestern Atlantic ◽  
Temporal And Spatial Patterns ◽  
Temporal And Spatial
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