Lake models John Boyle
Lakes trap particles and surface-active solutes, reducing landscape fluxes
Loch of Skene
The sedimented particles provide a record of changing fluxes
Lake models John Boyle
Three conceptual models Naumanns classification Pearsalls natural eutrophication Wetzels ecosystem concept of lakes
And one quantitative model: nutrient capture by lakes Simple box model Issues with the simple box model
Quantifying external loading Sediment focusing and measurement of P
burial The P retention concept
Loch Grannoch
Lake models Some conceptual models Naumanns classification
Deep Low rate of primary production Clear water Low algal growth Low littoral macrophytes, low
biomass, and low diversity
Shallow High rate of primary production Clear water Low algal growth High littoral macrophytes, high
biomass, high diversity
Oligotrophic Eutrophic
Einar Naumann, University of Lund, established the notion of lake trophic status in the 1920s based on the study of algae
High rate of primary production
Turbid water High algal growth,
high biomass, low diversity
Culturally eutrophic
Now we must add
Lake models Some conceptual models Pearsalls natural eutrophication
Immediately following formation, there is
low organic matter supply from the
immature freshly exposed catchment. The
lake is ultra-oligotrophic.
As catchment soils mature, there is growing
nutrient supply. And, as the aquatic
ecosystem matures, nutrients are trapped in
the lake system, leading to increasingly
autotrophic production.
As the lake fills in with sediment (some tens
of thousands of year after formation), the
decreasing water depth leads to a
disproportionate increase in trophic status.
William Pearsall (1891-1964) developed the still influential idea that lakes and lake basins become modified as they increase in age (Pearsall, 1921)
Lake models Some conceptual models Robert Wetzels ecosystem concept of lakes
From Wetzel (1983) Limnology
Leakage of nutrients from the wetland-littoral belt drives pelagial production
Lake models
In a deep, steep-sided, lake most of
the supplied particles settle quickly to
the sediment and are lost from the
lake system.
This can also explain Pearsalls aging lakes.
In a shallow-margined lake, allochtonous
particles are trapped by the wetland littoral
zone and converted into dissolved nutrient
that can be used by algae in the lake.
Some conceptual models Robert Wetzels ecosystem concept of lakes
Wetzels conceptual model explains Naumanns observation
Lake models John Boyle
Three conceptual models Naumanns classification Pearsalls natural eutrophication Wetzels ecosystem concept of lakes
And one quantitative model: nutrient capture by lakes Simple box model Issues with the simple box model
Quantifying external loading Sediment focusing and measurement of P
burial The P retention concept
Loch Grannoch
Lake models A quantitative model: nutrient capture by lakes Simple box model
P fluxes (or loadings, L) in a box model
Lin
Lsed
Lout
Lin = Lsed + Lout (inflow loading = sediment loading + outflow loading)
Lin = qin TPin where qin is the water influx,
and TPin is the TP concentration of inflow water
Lout = qout TPout where qout is the water
influx, and TPout is the TP concentration of outflow
water
Lsed = SR Psed where SR is the sediment mass accumulation rate, and Psed is the sediment P concentration
Issues with the simple box model Quantifying external loading Sediment focusing and measurement of P burial The P retention concept
Lake models A quantitative model: nutrient capture by lakes Issues with the simple box model Quantifying external loading
Lewis et al., 2013 Data for River Lee,
County Cork
Fluvial P transport show great temporal variability. This makes it difficult to obtain accurate total fluvial loads. Other sources of P are harder to quantify accurately. It is therefore difficult to balance P budgets.
Lake models A quantitative model: nutrient capture by lakes Issues with the simple box model Sediment focusing and measurement of P burial
If lakes were flat bottomed, and lake water well-mixed, the mean lake sediment P load would be easy. But
So, a focusing model is required to find mean values
Lake models A quantitative model: nutrient capture by lakes Issues with the simple box model Sediment focusing and measurement of P burial
Total sediment accumulation (1900-1983) = Either, Mean with zeros Lake area Or, Mean measured accumulating area (z>2m ?)
Esthwaite Water
The way forwards? 1. Dont pick lakes with complex
shape/bathymetry 2. Make good bathymetric maps 3. Use multiple cores and interpolate using a
simple hypsometric model of sediment accumulation
4. Use 210Pb inventory as a measure of focusing
Kassjn
Lake models A quantitative model: nutrient capture by lakes Issues with the simple box model The P retention concept
A number of people, notably Richard Vollenweider and Peter Dillon, developed lake P budget models built around a phosphorus retention coefficient, Rp. Rp = (Lin Lout)/Lin = Lsed/Lin
This is very useful if we want to reconstruct the landscape P flux (Lin, seen from the lake perspective) from the sediment record (Lsed): Lin = Lsed/Rp
And, if we know, or can estimate, past values of water flux, then we can estimate mean total P concentration: TP = Lin /qin = Lsed/(qin.Rp)
So, can we predict Rp?
Lake models A quantitative model: nutrient capture by lakes Issues with the simple box model The P retention concept So, can we predict Rp?
Rp=v/(1+v) (v = P sedimentation coeff. m yr-1) (derived from Vollenweiders model)
But, v (m yr-1) = k (m3 g-1).SR (g m-2 yr-1) and SR varies greatly between lakes
Lake models John Boyle
Three conceptual models Naumanns classification Pearsalls natural eutrophication Wetzels ecosystem concept of lakes
And one quantitative model: nutrient capture by lakes Simple box model Issues with the simple box model
Quantifying external loading Sediment focusing and measurement of P
burial The P retention concept
Loch Grannoch