Spatially heterogeneous trends in nearshore and offshore chlorophyll a concentrations in lakes Michigan and Huron (1998–2013)

Abstract

1. Nutrient abatement programmes have been successfully implemented around the globe to reduce nutrient loading into aquatic ecosystems. Concurrently, the worldwide spread of invasive filter feeders, such as dreissenid mussels, may alter nutrient dynamics in invaded systems by sequestering nutrients away from pelagic zones and reducing primary production in offshore areas. Such is the case in the Laurentian Great Lakes of North America, where decades of nutrient abatement and the establishment of dreissenid mussels have seemingly resulted in more oligotrophic conditions and altered spatial patterns of nutrient availability and primary production.2. Recent studies have focused on whole lake trends in primary production despite spatial differences in tributary inputs, bathymetry, and other environmental conditions that can affect primary production in nearshore areas. Thus, we hypothesised that trends in nearshore chlorophyll concentrations in different areas may diverge in a manner consistent with spatial differences in nutrient input. To evaluate these differences in surface chlorophyll responses, we assessed temporal trends in four different areas of Lake Michigan and three different areas of Lake Huron.3. We hypothesised that in lakes Huron and Michigan, nearshore zones have experienced slower declines of chlorophyll concentrations relative to offshore zones.To assess this hypothesis, we estimated temporal trends of surface water chlorophyll concentrations (a proxy for primary production) from satellite imagery from 1998 to 2013. We calculated average surface chlorophyll concentrations for 10-m depth intervals ranging from the shore (0-10 m) to offshore (>90 m) during representative months of May, July, and September. We then analysed these data to determine if long-term trends in surface chlorophyll varied by season, proximity to the shoreline, and water depth.4. The rates of annual change in chlorophyll concentrations in nearshore areas were markedly different to offshore trends in both lakes. Chlorophyll concentrations declined overtime in offshore areas, but nearshore chlorophyll concentrations were either stable (in May) or increased (in July and September) throughout the time series. | 367 STADIG eT Al.

Combined Earth observations reveal the sequence of conditions leading to a large algal bloom in Lake Geneva

“…Littoral zones have been acknowledged for their strong contribution in the lake productivity in small ecosystems 57 , 58 , but, compared to pelagic zones, have been undervalued in large lakes. Recent studies indicated that littoral zones of large low-nutrient water bodies can turn into phytoplankton production hot-spots with usually higher C chl-a than pelagic zones and spatially heterogeneous trends 59 , 60 .…”

“…The following procedure was implemented: Soil and sediment: CaCO 3 was removed by successive additions of 10 µL of 1 N HCl, under binocular magnifier, in the EA capsule. Then capsules were freeze-dried, closed, and introduced in the ECHoMICADAS gas source through the EA-GIS interface 59 . In addition, to simulate the action of waves, soil samples (40 g) were shaked (200 rpm) in distilled water (200 mL) for 7 days at 25 °C in the dark and dissolved organic carbon was processed as below.…”

Predicting larval alewife transport in Lake Michigan using hydrodynamic and Lagrangian particle dispersion models

“…Potential nursery habitat can vary widely with respect to temperature and productivity (Höök et al 2007; Stadig et al 2020), which reinforces the potential criticality of larval alewife being transported into different regions. Alewife are known to spawn on both the eastern and western coasts of Lake Michigan, in addition to connected tributaries and drowned river mouths (Goodyear 1982).…”

Evaluación ambiental de las riberas del lago Nahuel Huapi y propuesta de un índice de calidad de costas

“…No obstante, ante concentraciones intermedias a bajas de nutrientes, pero en ambientes poco expuestos al viento (como bahías cerradas, sitio 11), la acumulación de biomasa también puede verse favorecida. Es necesario destacar que en un lago con una superficie amplia como la del Nahuel Huapi (557 km 2 ), la concentración de clorofila varía muchísimo si se toma en sectores costeros o en sectores pelágicos del cuerpo de agua (Stadig et al 2019). En una columna de agua profunda, como es el caso de este lago, estos efectos se ven disminuidos por la complejidad de procesos que ocurren en ella.…”