PREDICTION OF DISSOLVED INORGANIC NITROGEN (DIN) CONCENTRATIONS IN DEEP, SEASONALLY STRATIFIED LAKES BASED ON RATES OF DIN INPUT AND N-REMOVAL PROCESSES
P. Hohener et R. Gachter, PREDICTION OF DISSOLVED INORGANIC NITROGEN (DIN) CONCENTRATIONS IN DEEP, SEASONALLY STRATIFIED LAKES BASED ON RATES OF DIN INPUT AND N-REMOVAL PROCESSES, Aquatic sciences, 55(2), 1993, pp. 112-131
Citations number
47
Categorie Soggetti
Water Resources",Limnology,"Marine & Freshwater Biology
Mean dissolved inorganic nitrogen concentrations ([DIN]) in deep, seas
onally stratified lakes with comparable DIN inputs can differ by up to
a factor of 3 depending on hydraulic and morphometric properties and/
or different trophic states of the lakes. In such lakes, net N sedimen
tation rates were estimated with two independent methods (sediment cor
e analysis and input-output mass balances). They were higher in eutrop
hic lakes (Mean: 5.1; SD: +/- 1.6 g m-2 yr-1; n = 13) than in oligotro
phic lakes (1.6 +/- 1.0 g m-2 yr-1; n = 3), but independent of [DIN].
Gaseous N loss rates to the atmosphere, as calculated from combined N-
and P-mass balances from selected lakes, ranged from 0.9 to 37.4 g m-
2 yr-1 (n = 10) and were positively correlated with [DIN]. Reduction o
f NO3- to N2 is assumed to be the main cause for gaseous N losses. A s
imple one-box mass balance model for [DIN], based on DIN input and rat
es and kinetics of N removal processes (net sedimentation and gaseous
N loss) is proposed, and validated with a data base on [DIN] and DIN i
nput in 19 deep, seasonally stratified lakes of central Europe. The mo
del illustrated that the amount of water loading per unit surface area
of a lake (called water discharge height q) is the critical parameter
determining mean lake [DIN] relative to mean input [DIN]. Lakes with
a q > 50 m yr-1 have average [DIN] similar to the [DIN] of the inflows
regardless of their trophic states, because input and outflow exceed
lake-internal N removal processes. A high primary production favors DI
N removal in lakes with q < 50 m yr-1. It is concluded that measures t
o decrease primary production, e.g. by means of P removal programs, le
ad to an increase of [DIN] in lakes.