Does browning affect the identity of limiting nutrients in lakes?

• Concentrations of dissolved organic carbon (DOC) have increased recently in many lakes at high latitudes in North America and Europe, but it is unclear what effect this will have on the identity of the limiting nutrient for phytoplankton [nitrogen (N) vs. phosphorus (P)]. Identifying the effect of changing DOC on phytoplankton nutrient limitation is complicated by spatial covariation between atmospheric N deposition and increasing DOC in areas where lake browning occurs. We conducted nutrient-limitation assays in 27 lakes from three sites along gradients of climate and atmospheric N deposition in Sweden. Within each site, lakes were selected to represent the range of DOC concentrations. We also conducted statistical analyses of large-scale lake survey data (n = 4768 lakes divided into 47 regions) to investigate relationships between DOC and nutrient stoichiometry while controlling for differences in N deposition. Our findings confirmed that most lakes were dual-limited by both N and P in the south, whereas northern lakes were primarily N-limited. Throughout Sweden the ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (TP) declined with increasing DOC in most regions, suggesting that browner lakes are more likely to be N limited. These results were not supported by our nutrient limitation assays, which identified no relationship between DOC and relative strength of limitation by N or P. Increased DOC also resulted in significant increases in both total and inorganic N and P fractions, suggesting that other factors such as light limitation or increased top-down control become more important as DOC increases.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

Arctic lakes

Boreal lakes

Dissolved organic carbon

Nitrogen

Phosphorus

Phytoplankton Sweden

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