Stephen L. Katz

Sixty years of environmental change in the world's largest freshwater lake – Lake Baikal, Siberia

High-resolution data collected over the past 60 years by a single family of Siberian scientists on Lake Baikal reveal significant warming of surface waters and long-term changes in the basal food web of the worlds largest, most ancient lake. Attaining depths over 1.6 km, Lake Baikal is the deepest and most voluminous of the worlds great lakes. Increases in average water temperature (1.21 °C since 1946), chlorophyll a (300% since 1979), and an influential group of zooplankton grazers (335% increase in cladocerans since 1946) may have important implications for nutrient cycling and food web dynamics. Results from multivariate autoregressive (MAR) modeling suggest that cladocerans increased strongly in response to temperature but not to algal biomass, and cladocerans depressed some algal resources without observable fertilization effects. Changes in Lake Baikal are particularly significant as an integrated signal of long-term regional warming, because this lake is expected to be among those most resistant to climate change due to its tremendous volume. These findings highlight the importance of accessible, long-term monitoring data for understanding ecosystem response to large-scale stressors such as climate change.

Observational Evidence of Spatial and Temporal Structure in a Sympatric Anadromous (Winter Steelhead) and Resident Rainbow Trout Mating System on the Olympic Peninsula, Washington

We documented the spawning distribution and male mating tactics of sympatric anadromous rainbow trout Oncorhynchus mykiss (winter steelhead) and resident rainbow trout in the Calawah and Sol Duc River basins, Washington. Snorkel surveys and in situ behavioral observations were used to determine the spatial and temporal distribution patterns and male mating tactics of anadromous, resident, and hatchery residual fish across the spawning season. In general, male steelhead entered our survey reaches earlier than female steelhead, and both entered earlier than the wild resident and hatchery residual forms. Spatially, wild residents represented the greatest proportion of the population in the middle and upper survey reaches. Those differences coincided with mating attempts primarily between male and female steelhead early in the spawning season and primarily between female steelhead and wild resident males at the end of the season. Most of the mating attempts that we observed involved a single female and a single male steelhead, but attempts commonly included multiple male steelhead, wild resident males, or both, and behavioral tactics differed between forms. The patterns suggest a strong temporal structure and a lesser spatial structure to the distribution of O. mykiss during the spawning season, which has important implications for future studies of this complex species.

Quantifying effects of abiotic and biotic drivers on community dynamics with multivariate autoregressive (MAR) models

Long-term ecological data sets present opportunities for identifying drivers of community dynamics and quantifying their effects through time series analysis. Multivariate autoregressive (MAR) models are well known in many other disciplines, such as econometrics, but widespread adoption of MAR methods in ecology and natural resource management has been much slower despite some widely cited ecological examples. Here we review previous ecological applications of MAR models and highlight their ability to identify abiotic and biotic drivers of population dynamics, as well as community-level stability metrics, from long-term empirical observations. Thus far, MAR models have been used mainly with data from freshwater plankton communities; we examine the obstacles that may be hindering adoption in other systems and suggest practical modifications that will improve MAR models for broader application. Many of these modifications are already well known in other fields in which MAR models are common, although they are frequently described under different names. In an effort to make MAR models more accessible to ecologists, we include a worked example using recently developed R packages (MAR1 and MARSS), freely available and open-access software.

Shifting regimes and changing interactions in the Lake Washington, U.S.A., plankton community from 1962-1994.

Understanding how changing climate, nutrient regimes, and invasive species shift food web structure is critically important in ecology. Most analytical approaches, however, assume static species interactions and environmental effects across time. Therefore, we applied multivariate autoregressive (MAR) models in a moving window context to test for shifting plankton community interactions and effects of environmental variables on plankton abundance in Lake Washington, U.S.A. from 1962–1994, following reduced nutrient loading in the 1960s and the rise of Daphnia in the 1970s. The moving-window MAR (mwMAR) approach showed shifts in the strengths of interactions between Daphnia, a dominant grazer, and other plankton taxa between a high nutrient, Oscillatoria-dominated regime and a low nutrient, Daphnia-dominated regime. The approach also highlighted the inhibiting influence of the cyanobacterium Oscillatoria on other plankton taxa in the community. Overall community stability was lowest during the period of elevated nutrient loading and Oscillatoria dominance. Despite recent warming of the lake, we found no evidence that anomalous temperatures impacted plankton abundance. Our results suggest mwMAR modeling is a useful approach that can be applied across diverse ecosystems, when questions involve shifting relationships within food webs, and among species and abiotic drivers.

Influence of Long-Distance Climate Teleconnection on Seasonality of Water Temperature in the World's Largest Lake - Lake Baikal, Siberia

Large-scale climate change is superimposed on interacting patterns of climate variability that fluctuate on numerous temporal and spatial scales—elements of which, such as seasonal timing, may have important impacts on local and regional ecosystem forcing. Lake Baikal in Siberia is not only the worlds largest and most biologically diverse lake, but it has exceptionally strong seasonal structure in ecosystem dynamics that may be dramatically affected by fluctuations in seasonal timing. We applied time-frequency analysis to a near-continuous, 58-year record of water temperature from Lake Baikal to examine how seasonality in the lake has fluctuated over the past half century and to infer underlying mechanisms. On decadal scales, the timing of seasonal onset strongly corresponds with deviation in the zonal wind intensity as described by length of day (LOD); on shorter scales, these temperature patterns shift in concert with the El Nino-Southern Oscillation (ENSO). Importantly, the connection between ENSO and Lake Baikal is gated by the cool and warm periods of the Pacific Decadal Oscillation (PDO). Large-scale climatic phenomena affecting Siberia are apparent in Lake Baikal surface water temperature data, dynamics resulting from jet stream and storm track variability in central Asia and across the Northern Hemisphere.

The Challenges of Tracking Habitat Restoration at Various Spatial Scales

Evaluating the ecological effectiveness of the hundreds of millions of dollars invested to recover Pacific Northwest salmon has a number of prerequisites— principally, detailed knowledge of management actions. In the absence of coordinated ecological monitoring, basic restoration project metadata (type, location, timing, etc.) is the primary source of information guiding restoration planning and management decisions. There are surprisingly few sources of habitat restoration information at scales appropriate to salmon recovery, ranging from small sub-watersheds to multistate evolutionarily significant units. We evaluate the consistency of two Columbia River basin restoration inventories developed in different ways but similar in goal: to inform future project placement. We compared the Pacific Northwest Habitat Project Database, compiled by researchers at NOAA Fisheries Service, and the Subbasin Inventories, compiled by local entities within each of 62 subbasins. Confederating these two data holdings, we f...