Bioavailability of macro-nutrients in Swedish Baltic Sea river catchments

Abstract

Popular science summary

Determination of nutrient bioavailability in Swedish rivers

Rivers deliver substantial amounts of carbon, nitrogen and phosphorus to coastal waters of the Baltic Sea. Depending on their bioavailability, inputs of C, N and P may in a significant way affect aquatic ecosystem. Determination of bioavailable fractions of C, N and P will allow action plans to address the problem of eutrophication correctly.

Eutrophication and nutrient overload is one of the biggest threats to the coastal waters of the Baltic Sea. Many monitoring programs were focusing on the total fractions of nutrients, however it seems that the bioavailable fractions of C, N and P are the most important for the microbial activities.

In previous studies nutrient bioavailability has been measured using a variety of methods which often lead to inconsistent results. To simplify the methodology and to overcome differences between previous approaches a new method was used. Bacterial production (BP) was measured in response to limiting nutrient addition (nutrient spike). On the basis of response curve, where BP was on the y-axis and increasing concentrations of limiting nutrient, the bioavailable fraction of nutrient was calculated. To our knowledge there are no other published studies on estimating bioavailable C, N and P simultaneously using a similar approach.

Results show that bioavailability of carbon found in nine studied rivers is low. The reason could be that samples were obtained during the base flow conditions when terrestrial origin carbon seems to be more refractory. Low bioavailability of carbon also affected the nutrient balance in rivers. Opposite to expected, three rivers were primarily carbon limited. Source for the bioavailable nitrogen was different between southern and northern part of Sweden. In the south, dissolved inorganic nitrogen (most plausibly coming from the agriculture runoff) was covering the nitrogen demand. In the north, dissolved organic nitrogen was the only source for the BN. The results from the phosphorus bioavailability (BAP), which were compared with other studies performed on the same river systems, showed that BAP has strong implications for the bacterial metabolism.

These results show that studies about nutrient bioavailability may have important implications for the conservation programs concerning problem of the eutrophication. In particular bioavailable phosphorus seems to have a direct effect on bacteria activities. Moreover dissolved organic nitrogen, which was often neglected as a part of bioavailable fraction, could be an important source of nutrient for the biota in the coastal areas. Studies concerning the carbon bioavailability deserve further investigation, especially in respect to the seasonality.

Advisor: Martin Berggren, Emma Kritzberg
Master´s Degree Project 30 credits in Conservation Biology, 2014
Department of Biology, Lund University

Abstract

Abstract

Rivers deliver substantial amounts of carbon (C), nitrogen (N) and phosphorus (P) to estuaries, but the effects of these inputs on the ecosystem depend on the degree to which the nutrients are bioavailable. The nutrient bioavailability is poorly known in northern regions of Scandinavia where most of the nutrients are organic. To simplify the measurements of nutrient bioavailability and to overcome methodological artifacts from previous studies, I used a recently developed framework. I determined bioavailable C, N and P simultaneously, using consistent methods. First, C, N and P-limited bacterial growth was induced in three parallel batch cultures. The amount of bacterial production (BP) was then recorded per unit of limiting nutrient (C, N or P) in 7-day incubations spiked with different concentrations of glucose, ammonium nitrate and orthophosphate, respectively. Once the BP yield per unit of C, N and P was established the respective bioavailable nutrient was calculated. BP could be used as an experimental response variable to determine the bioavailable nutrient fractions in natural water samples. Measurements were performed in 9 Swedish rivers.

The results show that bioavailability of carbon found in the nine studied rivers was low. The reason could be that the samples were obtained during the base flow conditions when terrestrial origin carbon seems to be more refractory. Low bioavailability of carbon also affected the nutrient balance in rivers. Opposite to what was expected, three rivers were primarily carbon limited. The source for the bioavailable nitrogen (BN) was different between the southern and northern parts of Sweden. In the south, dissolved inorganic nitrogen, most plausibly coming from the agriculture runoff, was covering the nitrogen demand. In the north, dissolved organic nitrogen was the only source for the BN. The results from the phosphorus bioavailability (BAP), which were compared with other studies performed on the same river systems, showed that BAP has a strong impact on the bacterial metabolism.

These results show that studies about nutrient bioavailability may have important implications for the conservation programs concerning the problem of eutrophication. In particular, bioavailable phosphorus seems to have a direct effect on bacterial activities. Moreover, dissolved organic nitrogen, which was often neglected as a part of the bioavailable fraction, could be an important source of nutrient for the biota in the coastal areas. Studies concerning the carbon bioavailability deserve further investigation, especially in respect to the seasonality.

• author: Marchlewska, Joanna
• supervisor: Martin Berggren; Emma Kritzberg
• organization: Degree Projects in Biology
• course: BIOM24 20131
• year: 2014
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 4406764
• date added to LUP: 2014-04-24 16:17:25
• date last changed: 2014-04-24 16:17:25