Food Webs and Fish Size Patterns in Insular Lakes Partially Support Climate-Related Features in Continental Lakes

Disentangling the effects of climate change on nature is one of the main challenges facing ecologists nowadays. Warmer climates forces strong effects on lake biota for fish, leading to a reduction in size, changes in diet, more frequent reproduction, and stronger cascading effects. Space-for-time substitution studies (SFTS) are often used to unravel climate effects on lakes biota; however, results from continental lakes are potentially confounded by biogeographical and evolutionary differences, also leading to an overall higher fish species richness in warm lakes. Such differences may not be found in lakes on remote islands, where natural fish free lakes have been subjected to stocking only during the past few hundred years. We studied 20 species-poor lakes located in two remote island groups with contrasting climates, but similar seasonality: the Faroe Islands (cold; 6.5 ± 2.8 °C annual average (SD) and the Azores Islands (warm; 17.3 ± 2.9 °C)). As for mainland lakes, mean body size of fish in the warmer lakes were smaller overall, and phytoplankton per unit of phosphorus higher. The δ13C carbon range for basal organisms, and for the whole food web, appeared wider in colder lakes. In contrast to previous works in continental fresh waters, Layman metrics of the fish food web were similar between the two climatic regions. Our results from insular systems provide further evidence that ambient temperatures, at least partially, drive the changes in fish size structure and the cascading effects found along latitude gradients in lakes.

Increased relative abundance of colonial scaled chrysophytes since pre-industrial times in minimally disturbed lakes from the Experimental Lakes Area, Ontario

A top–bottom paleolimnological analysis of 30 undisturbed lakes in the Experimental Lakes Area (ELA) in northwest Ontario showed marked increases in the relative abundance of colonial scaled chrysophyte taxa in most lakes since pre-industrial times. The increase in abundance of colonial taxa was primarily driven by Synura sphagnicola in small, high-nutrient, and warm lakes. The colonial taxa Synura petersenii and Synura echinulata also increased in the deeper study lakes. Detailed analysis of sediment cores from six lakes revealed that these changes occurred in the early to mid-1900s. Based on the modern distribution of scaled chrysophytes relative to lake physicochemical data, we propose multiple processes that may be contributing to these changes, such as changes in lake thermal properties and historical changes in the flux of important particles and solutes to lakes. Additional mechanisms that may contribute to the observed changes are discussed, including trophic interactions and changes in limnetic pCO2. Because the ELA is relatively undisturbed, our findings provide important information on the drivers responsible for increases in colonial chrysophyte abundance, which have been documented in studies of lakes in central Ontario and northeast United States.

Temperature-dependence of the relationship between <i>p</i>CO₂ and dissolved organic carbon in lakes

The relationship between the partial pressure of carbon dioxide (pCO2) and dissolved organic carbon (DOC) concentration in Brazilian lakes, encompassing 225 samples across a wide latitudinal range in the tropics, was tested. Unlike the positive relationship reported for lake waters, which was largely based on temperate lakes, we found no significant relationship for tropical and subtropical Brazilian lakes, despite very broad ranges in both pCO2 and DOC. Closer examination showed that the strength of pCO2 vs. DOC relationships declines with increasing water temperature, suggesting substantial differences in carbon cycling in warm lakes, which must be considered when upscaling limnetic carbon cycling to global scales.

The distribution of four Chaoborus species (Diptera: Chaoboridae) along an elevation gradient in Canadian Rocky Mountain lakes

We tested the hypothesis that the distribution of four species of Chaoborus is limited by water temperature in Rocky Mountain lakes. Midsummer surface water temperature (MSSWT) of Rocky Mountain lakes varied between 25 and 5 °C along an elevation gradient spanning 600–2400 m above sea level. Chaoborus (subgenus Chaoborus) americanus and C. (C.) flavicans were collected in lakes with MSSWT ≥ 16 °C, generally corresponding to lakes at elevations lower than 1600 m above sea level. Chaoborus (Sayomyia) punctipennis was only collected in warm lakes (MSSWT ≥ 21 °C). Species of the subgenus Schadonophasma (C. trivittatus and possibly C. cooki) were not commonly collected, but preliminary data suggest that they may be more tolerant of low water temperatures than the other species. On a qualitative basis, the distribution of these chaoborids in the Rockies is similar to their latitudinal distribution. However, MSSWT as a valid predictor of Chaoborus species distribution with latitude remains to be tested. The gradient in lake temperature found in mountainous environments appears to be a useful gauge for obtaining information about the distribution of invertebrates relative to temperature.

Projected Distribution of the Zebra Mussel, Dreissena polymorpha, in North America

An analysis of the European distribution of the zebra mussel, Dreissena polymorpha, shows that the species probably will spread over much of North America. Only softwater districts and the extreme northern and southern parts of the continent are unlikely to be colonized. Within this range, D. polymorpha is most likely to be found in large, hardwater lakes and in running waters more than 30 m wide. Populations of D. polymorpha probably will spread over a larger part of the lake bottom in shallow, warm lakes than in deep, cold lakes. I could not make any predictions about the expected population densities of D. polymorpha in either lakes or streams.

Holocene paleohydrology of central Alberta: testing the general-circulation-model climate simulations

Paleoecological investigations of 28 lakes and bogs provide the basis for a Holocene paleohydrological record for central Alberta. Shallow basins, empty during the early Holocene, began flooding shortly after 8000 years ago; most filled from 6500 to 4500 years ago, and none filled later than 3000 years ago. Pollen of a hypersaline indicator genus, Ruppia, was found in cores of lakes where the plant does not presently grow, indicating lower lake levels, evaporation stress, and increased salinity from 8000 to 3000 years ago. Moore Lake (54°30′N, 100°30′W) may have dropped 15 m from 9200 to 5900 years ago, and Lofty Lake (54°44′N, 112°29′W) largely dried up between 8700 and 6300 years ago. Lower water levels are suggested for several lakes by shifts in fossil diatom populations from planktonic to benthic, particularly epipelic species including pioneering taxa. These shallow, warm lakes were highly productive and sedimentary pigment levels reached maximum values between about 9000 and 4000 years ago.The paleohydrological record indicates early Holocene aridity, with the onset and development of moister conditions between 8000 and 3000 years ago, by which time modern climatic and vegetation conditions had been established. This record fits the Holocene climate predicted by the general-circulation-model simulations based on orbital perturbations.