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Insight into the causes and consequences of changes in aquatic biodiversity requires an improved understanding of the nature of the relationships between species richness and ecosystem function over a much longer temporal perspective than we currently possess. We used high-resolution paleoecological records from two prairie lakes to show that diatom species richness (as fossil frustules) was negatively correlated ([r.sup.2] = 0.09-0.24, p < 0.001) with diatom production (as fossil pigments) during the past 2,000 yr. By comparing analyses from intervals of fresh and saline waters, we demonstrate that these significant richness production relationships arose during freshwater periods ([r.sup.2] = 0.13-0.45, p < 0.001) and could be eliminated ([r.sup.2] < 0.02, p > 0. I) by abiotic disturbances such as droughts. Procrustes analyses of the concordance of species change within freshwater communities and the change in richness--production relationships through time revealed that shifts in diatom community composition could have a large influence in determining the negative relationship between richness and production. Finally, significant correlations ([r.sup.2] = 0.09-24, p < 0.0001) between past diatom species richness and ratios of stable isotopes (primarily [[delta].sup.15]N) suggested that C and N biogeochemical cycles are also linked to changes in algal biodiversity. Taken together, these analyses suggest that the ongoing disruption of climate and biogeochemical systems by humans may obscure the relationship between aquatic biodiversity and ecosystem function in the future.

A more integrated paradigm would be revived if dissolved organic carbon and nutrients were again seen as regulators of lake ecosystems. Trophic status is the main interpretive paradigm in studying lakes. Lake characterization should extend beyond the nutrient-productivity paradigm. Numerous threats to lake ecosystems are recognized. A paradigm that includes colored dissolved organic carbon. CDOC as well as nutrients would be useful in predicting and understanding response of lake ecosystems to multiple stressors. Some operational definitions that allow for placing some of the major lake types on the axes would be added. Data from various lakes and a successional sequence in Glacier Bay, AK, illustrate potential usefulness of the 2-axis model in separating lake types.

We investigated changes in UV attenuation and macrozooplankton community structure in a set of lakes along a deglaciation chronosequence in Glacier Bay Alaska. Terrestrial succession in the watersheds of these lakes results in increasing dissolved organic carbon (DOC) content over time. Due to the primary role of DOC in controlling UV attenuation in lakes, one would suspect a gradient in UV attenuation and potentially zooplankton community structure in lakes of different ages. Field measurements of UV in seven lakes of different ages revealed that UV attenuation depths (1% of surface irradiance at 320 nm) ranged from 0.6 m in the oldest lake in the set (90 yr old), to more than 14 m in the youngest lake (10 yr old). Zooplankton community structure also changed across lakes of different ages. Patterns of distribution and abundance of the zooplankton both among and within lakes were consistent with the hypothesis that UV influences zooplankton community structure. The major differences in species composition among lakes were the absence of two primarily epilimnetic species (Asplanchna priodonta and Ceriodaphnia quadrangula) in all but the oldest lake, and the absence of Bosrnina longirostris in the four youngest lakes. Transplant experiments in which UV radiation was manipulated in situ revealed that all three of these 'delayed colonizer' species perish within only a few days when exposed to UV levels found in the surface waters (0.5 m depth) of the youngest lake. The strong dependence of UV radiation transparency on terrestrially derived DOC suggests a linkage between development of terrestrial plant communities within the watershed, changes in lake hydrology, and the early succession of zooplankton communities following deglaciation. Key words: deglaciation; dissolved organic carbon; Glacier Bay, Alaska; lake ontogeny; predation; succession; ultraviolet radiation; zooplankton community.