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Nutrient Concentrations In The Swina Strait During The Years 1996 And 1997 
With Emphasis On The Flood Event 
Marianna Pastuszak, Stanislaw Sitek & Alfred Grelowski 
Sea Fisheries Institute 
ul. Kollataja 1 
81 332 Gdynia 
Abstract 
The Swina Strait is on the one hand, draining water from the Szczecin Lagoon, the latter being 
a recipient of the Odra river waters, on the other hand it is under frequent and variable inflows 
of salt water from the Pomeranian Bay. Salinity, temperature, oxygen content, nitrates, nitrites, 
ammonia, phosphates, total nitrogen and total phosphorus were measured 1 km upstream from 
the Swina outlet over the period March 1996 - December 1997. 
Surface inorganic nitrogen concentrations were predominated by nitrates round the year with a 
maximum in winter/spring (well pronounced even over the vegetation period) and a minimum 
in summer (July/August). This pattern remained unchanged near the bottom with the excepti 
on of summer periods, in particular during the flood event when ammonia prevailed over nitra 
tes. Phosphate annual patterns show a maximum in winter which was followed by a drop in 
concentrations over the early summer period, and then by an increase over August/September, 
sometimes even October. The latter increase, which is a permanent phenomenon in the Szcze 
cin Lagoon, probably arises from intensive phosphate regeneration and limitation of primary 
production by low concentrations of nitrogen over the summer period in that region, and from 
the lower dilution factor during the summer periods. 
The flood disaster resulted in increased discharges of nitrogen and phosphorus into the Pome 
ranian Bay in the time period which is usually characterized by very low concentrations of nu 
trients and their limiting role in the Bay. Maximum concentrations of inorganic nitrogen (~ 56 
umol dm'-*) in the Swina Strait were comparable, while phosphates (~ 6 umol dm'3) slightly 
higher than maximum 1997 winter/spring values but their surface flood values were up to 20 
times and 2 times higher, respectively, in comparison with concentrations measured in compa 
rable period of 1996. Concentrations of nitrites during the flood were a few times higher than 
usually observed in the Swina Strait indicating bacterial activity. Total nitrogen (max. -180 
umol dm'-’) and total phosphorus (max. -10 pmol dm'3) concentrations during the flood were 
by 70% and about 2 times higher, respectively, in comparison with comparable 1996 values. 
Flood waters were carrying a lot of suspended matter which must have been undergoing sedi 
mentation. That fact, plus near-bottom saline water inflow, coinciding with high water tempe 
rature, led to water stratification and intensified biodegradation processes of suspended matter 
and resulted in an oxygen deficit, hydrogen sulphide formation, and high ammonia concentrati 
ons (-21 ¡umol *dm - 3 ) in the near the bottom layer of the Swina Strait. 
The consequences of the flood seem to be visible in autumn, expressed particularly by nitrogen 
concentrations, being 2-3 times higher as compared with the values for comparable time of 
1996.