Seaweed Nutrient Dynamics: Estuarial Ecosystems Study

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Table of Contents

Abstract
Introduction
Methods
Results
Discussions
Acknowledgements
Reference List

Abstract

Seaweeds are pertinent basic producers especially in low-lying coastal ecosystems. They particularly do well in the open end of the mouth of oceans called an estuary. The greatest importance of these aquatic plants is that the biomass produced by these species is estimated at over 400 times more than that obtained from other aquatic derivatives like phytoplankton. Besides, seaweed which exists alongside the tidal current of the sea may be highly generative. The yearly production of dry matter in a given area is in surplus of other forms of vegetation like forests. As a result, the ecophysiology of this aquatic vegetation is of great significance in our appreciating the coastal ecosystems.

Similar to phytoplankton, this plant obtains its vital growth nutrient basically from the surrounding waters. The nutrients needed by seaweed exists both in high and low concentrations. For instance, non-organic carbon has a higher concentration while elements such as nitrogen and phosphorus have relatively low levels of concentration. Indeed, nitrogen in this case is of utmost importance due to the fact that it controls growth rate o f the seaweed in such marine environment. Seaweeds will obtain the nutrients required by absorption through the thallus. Moreover, ammonia is also contained in non-organic nitrogen and is derived as waste product from the plants which are closely related with algae.

Introduction

Seaweeds obtain the nutrients they require for growth through the surrounding waters. The division of those resources which prove to be limiting is referred to as complementarity. Some of these resources include nitrogen, nitrites or ammonium compounds. This competition may easily result in general increase of resource overuse which may equally be imperative in the process of maintaining a state of balance in biodiversity (Gunson 1993). This practical part will investigate whether there exists this for of competition in seaweed. Additionally, the rates of nitrogen uptake by New Zealand seaweeds will be experimentally investigated and an analogy drawn with other geographical environments. Before the assimilation of any vital nutrient, the same has to go through a membrane. This is possible in two different ways namely through low affinity and high affinity transportation mechanisms. One of the categories of a low affinity is the one described by the linear relationship between uptake and the amount of concentration while the high affinity transport mechanism entails the transfer of materials across semi permeable membrane due the chemical difference between the two ends. The overall aim of this experiment is to investigate the relationship between seawater nutrient (ammonium and nitride) concentration and rates of nutrient uptake by a range of New Zealand seaweeds and the ability of the seaweeds to partition these sources of nitrogen.

Methods

A stock solution containing 50 mM ammonium chloride was provided. Thereafter, a dilution of the very stock solution followed. As a result, 100mL of seawater containing 50μM of a standard ammonium was obtained. Then, a series of 5 mL samples was prepared in labeled polypropylene scintillation vials containing 0, 10,20,30,40 and 50 μM ammonium in seawater. In each of the vials, the following were added namely o.5mL trisodium citrate, 1.0 mL phenol nitroprusside and 1.0 mL alkaline hypochloride. Then, the caps were screwed up on the vials and placed in a tray to allow the development of colour at a temperature of 40 degrees centigrade while in dark. This was left for 60 minutes before the final reading could e taken.

The second art of the experiment involved the preparation of ammonium uptake. After careful measurement, the required volume of ammonium solution was added to the seawater and thoroughly mixed. Thereafter, a 5 mL sample from each box was taken and each sample dispensed separately. The seaweed was then added and timing was started. The second 5 mL sample was taken 2.5 minutes after seaweed was added. As a precaution, both the seaweed and the sample were mixed thoroughly before the preceding sample was taken. The time course for each of the samples was set at 0, 2.5, 5, 7.5,10,15 and 20 minutes. After finishing the first time course, the seawater was discarded and a fresh course set up.

In experimenting on the nitride uptake, two Perspex boxes were provided which were used to incubate the seaweed. The box was thoroughly washed before the onset of the experiment and between each determination. The required volume of the nitride solution was added to seawater and thoroughly mixed. After mixing was complete, a 5 mL sample was taken and dispensed into each separately. This was taken as the zero time samples. Seaweed was then added and timing started. Before taking each sample, the seaweed and seawater were mixed thoroughly. The time course for each test was set at 0, 2.5, 5, 7.5,10,15 and 20 minutes respectively. In determining the nitride concentration in the nitride sample, each of the 5 mL samples was treated with 0.2 mL sulphanilamide and 0.2 mL of NEDA. The absorbance against the blank containing seawater only was then read and the two reagents after every 10 minutes.

Results

At the end of the experiment, it was found out that the rate uptake was directly proportional to the concentration of the solutions. For example at a concentration of 10.8216, the rate of uptake after an interval of 10 was found to be 0.2949 while after an interval of 20 minutes, the concentration had rose to 18.1511 while the calculated rate of uptake was 0.2191. After 40 minutes, the rate of uptake was standing at 1.7918 while concentration stood at 36.4961. The overall uptake coefficient was found to be 0.044119. On the same note, the concentration of the solutions against absorbance level depicted direct proportionality whereby concentration increased steadily with absorbance. For instance, at a concentration of zero, the absorbance was also zero while at a concentration of 20, absorbance was 1.76

Discussions

From the results obtained above, a graph of rate of nitrite uptake against nitrite consumed is a straight line passing through the origin. This depicts clearly the concept of complementarity and ecophysiology in which there is partitioning of the limiting resources. Since both nitrites and ammonium are vital nutrients and are also limited at the same time, both the seaweeds and phytoplankton will tend to compete for their uptake (Cometti & Morton 1985). A Similar trend is obsereved when a different geospatial set of data is considered. The assimilation of nutrients through a cell membrane in this case is affected by both low and high affinity transport system. This characteristic behaviour in which there is an overall increase in the consumption of resources is significant in maintaining biodiversity. As can be seen, complementarity can equally occur in seaweed assemblages (Bradstock 1989).

Acknowledgements

I would to express my sincere and heartfelt gratitude to my fellow group members and class mates for their valuable support and enduring effort in the course of these practical studies. I wish you all the best of success in your academic endeavors.

Reference List

Bradstock, M. (1989) between the tides: New Zealand shore and estuary life, David Bateman.

Cometti, R. & Morton, J. (1985) Margins of the sea: exploring New Zealand’s coastline, Hodder and Stoughton.

Gunson, D. (1993) A guide to the New Zealand seashore, Viking Pacific.

Little, C. & Kitching, J.A. (1996). The biology of rocky shores, Oxford University Press.

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