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About UNEP
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United Nations Environment Programme
Division of Technology, Industry and Economics
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Newsletter and Technical Publications
Freshwater Management Series No. 5

Guidelines for the Integrated Management of the Watershed
- Phytotechnology and Ecohydrology -


I. Overview of other possible ecohydrological modelling cases

The Cannaneia Estuary, Brasil: Ecosystems with pulsing patterns often have a greater level of biological activity and chemical cycling than systems with relatively constant patterns. In this case, the shores of the islands within the estuary and along the coast are very productive mangrove wetlands, and the entire estuary is an important nesting area for fish and shrimp. A channel was built to avoid upstream flooding, where productive agricultural lands are situated. The construction of the channel has caused a conflict between the farmers, who want the channel open, and fishermen, who want it closed because of its affect on the salinity of the estuary (the right salinity is of great importance for the mangrove wetlands). The estuary is exposed to tidal influences that are important for the maintenance of good water quality with a certain minimum salinity. The conflict could be resolved using an ecohydrological approach that takes advantages of the pulsing force (the tide). A sluice in the channel could be constructed to discharge the fresh water when it is least harmful to the mangrove, in which case the tides would be used to transport the fresh water as rapidly as possible out to sea. The model is constructed to determine when the sluice should be operated. Based on the analysis, it was recommended that the sluice be closed when the tide is on its way into the estuary and opened when the tide is on its way out to sea.

The Mondego Estuary, Portugal: Eutrophication has increased in the Mondego Estuary during the last decades due to the discharge of nutrient-rich fresh water from agricultural ands. The estuary is exposed to both these fresh water discharges and to tidal fluctuations. Consequently, in parts of the estuary, Enteromorpha spp. has replaced Zostera spp., and the annual variation within the Enteromorpha spp. community is strongly dependent on the amount of freshwater. Strong fresh water discharges decrease salinity, and low salinity inhibits the growth of the macroalga, despite the increased concentrations of nitrogen in the water column. Also, the dissolved nitrogen discharged in the freshwater from the mainland increases the N:P ratios, since phosphorus is released from sediment into the water column. The model relates the growth conditions of Enteromorpha spp. and Zostera spp. to the salinity and nutrient concentrations. By discharging fresh water through an already-constructed sluice at the time when Zostera spp. would have the best growth conditions (determined by a combination of salinity and nutrient concentrations) and Enteromorphaspp. the worst conditions, it would be possible, at least partially, to control the eutrophication of the estuary.

It is clear from these and other case studies that hydrology has an important effect on the biological components of an aquatic ecosystem. This effect can be utilised to improve the environmental management of aquatic ecosystems. The quantification of the magnitude of the effect is obviously advantageous, but its resolution is dependent upon the entire ecosystem with its high degree of inherent complexity. The usefulness of models in evaluating ecohydrological approaches to assessing such effects is apparent.

Appendix: Model Equations

PA(t) = PA(t - dt) + (PUP - PGR - PAS - PAOUT) * dt

INIT PA = 0.018

PUP = PA*PS*3*1.12^(20-temp)/(PS+0.08)

PGR = PZ*0.9*1.12^(20-temp)*(PA-0.001)/(PA+0.1)

PAS = PA*0.08

PAOUT = PA*qvout

PCF(t) = PCF(t - dt) + (PTP + spa2 - PCFMF) * dt

INIT PCF = 0.22

PTP = 0.007*PCF*1.1^(20-temp)*(PPF-0.01)/(PPF+0.01)

spa2 = PETP*0.035

PCFMF = 0.03*PCF+0.33*PTP

PD(t) = PD(t - dt) + (PZMF + PPFMF + PCFMF - PDS - PDMI - PDOUT) * dt

INIT PD = 0.07

PZMF = PZ*0.0024*1.07^(25-temp)+0.33*PGR

PPFMF = 0.012*PPF*1.1^(20-temp)+PPR*0.33

PCFMF = 0.03*PCF+0.33*PTP

PDS = 0.1*PD

PDMI = PD*0.1*1.1^(20-temp)

PDOUT = PD*qvout

PEPF(t) = PEPF(t - dt) + (SP1 - PEPFOUT - spa1) * dt

INIT PEPF = 0

SP1 = IF(TIME<180)THEN(0.075*PPF)ELSE(0)

PEPFOUT = PEPF*(qvout+0.28*1000000/VOLUME)

spa1 = PEPF*0.12

PETP(t) = PETP(t - dt) + (SP2 - PETPOUT - spa2) * dt

INIT PETP = 0

SP2 = IF(120<TIME<240)THEN(0.035*PCF)ELSE(0)

PETPOUT = PETP*(qvout+0.01*1000000/VOLUME)

spa2 = PETP*0.035

PPF(t) = PPF(t - dt) + (PPR + spa1 - PTP - PPFMF) * dt

INIT PPF = 0.11

PPR = PPF*0.04*1.12^(20-temp)*(PZ-0.01)/(PZ+0.02)

spa1 = PEPF*0.12

PTP = 0.007*PCF*1.1^(20-temp)*(PPF-0.01)/(PPF+0.01)

PPFMF = 0.012*PPF*1.1^(20-temp)+PPR*0.33

PPW(t) = PPW(t - dt) + (PSM - PPWD) * dt

INIT PPW = 0.04

PSM = PSED*0.08*1.1^(20-temp)

PPWD = PPW*0.09*1.06^(20-temp)

PS(t) = PS(t - dt) + (PIN + PDMI + PPWD - PUP - POUT) * dt

INIT PS = 0.04

PIN = PIQ*QV

PDMI = PD*0.1*1.1^(20-temp)

PPWD = PPW*0.09*1.06^(20-temp)

PUP = PA*PS*3*1.12^(20-temp)/(PS+0.08)

POUT = PS*qvout

PSED(t) = PSED(t - dt) + (PDS + PAS - NEXP - PSM) * dt

INIT PSED = 0.04

PDS = 0.1*PD

PAS = PA*0.08

NEXP = (PAS+PDS)*0.25

PSM = PSED*0.08*1.1^(20-temp)

PZ(t) = PZ(t - dt) + (PGR - PPR - PZMF) * dt

INIT PZ = 0.2

PGR = PZ*0.9*1.12^(20-temp)*(PA-0.001)/(PA+0.1)

PPR = PPF*0.04*1.12^(20-temp)*(PZ-0.01)/(PZ+0.02)

PZMF = PZ*0.0024*1.07^(25-temp)+0.33*PGR

VOLUME(t) = VOLUME(t - dt) + (INWAT - OUTWAT) * dt

INIT VOLUME = 1000000

INWAT = 1000000*QV

OUTWAT = 1000000*qvout

PIQ = 0.5

QV = GRAPH(TIME)

(0.00, 0.00), (15.9, 0.032), (31.7, 0.03), (47.6, 0.035), (63.5, 0.03), (79.3, 0.028), (95.2, 0.02), (111, 0.015), (127, 0.015), (143, 0.008), (159, 0.008), (175, 0.00), (190, 0.01), (206, 0.01), (222, 0.01), (238, 0.01), (254, 0.01), (270, 0.015), (286, 0.02), (302, 0.025), (317, 0.025), (333, 0.02), (349, 0.025), (365, 0.03)

qvout = GRAPH(TIME)

(0.00, 0.00), (36.5, 0.032), (73.0, 0.03), (110, 0.032), (146, 0.02), (182, 0.015), (219, 0.00), (256, 0.00), (292, 0.015), (328, 0.025), (365, 0.025)

temp = GRAPH(TIME)

(0.00, 0.00), (30.4, 0.00), (60.8, 2.20), (91.2, 5.80), (122, 12.7), (152, 16.5), (182, 19.8), (213, 22.4), (243, 18.7), (274, 15.2), (304, 9.80), (335, 5.40), (365, 1.00)

 

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