No abstract

Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer 'growing seasons'. We executed the first global quantitative synthesis on under-ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter-summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake-specific, species-specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass.

1. Dissolved organic carbon (DOC) plays a central role in the dynamics of stream and river ecosystems, affecting processes such as metabolism, the balance between autotrophy and heterotrophy, acidity, nutrient uptake and bioavailability of toxic compounds. However, despite its importance to stream processes, restoration and management activities rarely incorporate DOC as a major management criterion. 2. Lotic DOC pools reflect terrestrial organic carbon accumulation, transfer to the river channel and aquatic processing. In pristine landscapes, characteristics such as topography, climate, and landscape composition are strong predictors of terrestrial accumulation and transfer. Within aquatic systems, the quantity and form of DOC are altered by a variety of processes including primary production, microbial breakdown, sorption to particles and photodegradation. 3. Terrestrial accumulation, transfer and aquatic processing of DOC in agricultural and other human-dominated landscapes are all subject to substantial change. Consequently, DOC pools in agricultural streams likely differ from historic conditions and now include more labile material and low concentrations of a variety of ubiquitous synthetic organic compounds (e.g. pesticides, antibiotics). 4. Although DOC change in agricultural streams and associated ecological consequences are expected to be widespread, current understanding and relevant data needed to manage affected systems are surprisingly scarce. 5. Wetland and riparian restoration projects have variable effects on fluvial DOC regimes, but management at this intermediate scale is a realistic compromise between the small extent of most restoration projects and the large spatial scale over which organic carbon impairment occurs.

Global food production crucially depends on phosphorus (P). In agricultural and urban landscapes much P is anthropogenic, entering through trade. Here we present a long-term, largescale analysis of the dynamics of P entering and leaving soils and aquatic systems via a combination of trade, fluvial transport, and waste transport. We then report net annual P inputs,

Reproducibility is a key tenet of the scientific process that dictates the reliability and generality of results and methods. The complexities of ecological observations and data present novel challenges in satisfying needs for reproducibility and also transparency. Ecological systems are dynamic and heterogeneous, interacting with numerous factors that sculpt natural history and that investigators cannot completely control. Observations may be highly dependent on spatial and temporal context, making them very difficult to reproduce, but computational reproducibility can still be achieved. Computational reproducibility often refers to the ability to produce equivalent analytical outcomes from the same data set using the same code and software as the original study. When coded workflows are shared, authors and editors provide transparency for readers and allow other researchers to build directly and efficiently on primary work. These qualities may be especially important in ecological applications that have important or controversial implications for science, management, and policy. Expectations for computational reproducibility and transparency are shifting rapidly in the sciences. In this work, we highlight many of the unique challenges for ecology along with practical guidelines for reproducibility and transparency, as ecologists continue to participate in the stewardship of critical environmental information and ensure that research methods demonstrate integrity.