Hydrologic cycle

What are the inputs in the hydrological cycle

• Rain

  • Temporally vaiable, variable amount

• Snow

  • unavailable until melt

  • recharges surface soil and ground water in spring

• Fog and dew

  • limited to humid environments (redwood, cloud forests, etc.)

What are the outputs of the hydrologic cycle

Transpiration- dominant process

• goes through major flux based on LAI (between 2-18)

Also

• evaporation

• ground water seepage

• streamflow

What is the equation for evapotranspiration?

Evaporation (Surfaces- plants, soils) + Transpiration via stomata

What does hydraulic redistribution do?

Recharges surface and deeper soils nightly, delays seasonal soil drying (august and september)

How does interception vary by species?

Broadleaf species intercept more precip (48%) than conifers do (12%)

also varies where the precip lands- Broadleaf directs more water into stem via interception, while conifer has high canopy throughfall, and less funnel of water around stem

What effects the proportion of non-intercepted precip. that will be throughfall vs stemflow

Spacing and crown form

Equation of interception?

Intercepted= Total precip. - (throughfall + stemflow)

How does interception vary with rainfall event size?

In larger rainfall events, canopy storage maxes out and sends most precip crashing to forest floor

In smaller events, canopy may be able to intercept the entire event

What characteristics of forest ecosystems are likely to influence water and nutrient fluxes?

• Forest age

• disturbance

• nutrient identity (is the nutrient limiting or not?)

Why does nutrient conc. in streams vary with forest age?

• reduced uptake due to tree age

• differences in fine/coarse litter, decomposition

What happens to the hydrological cycle when the forest is disturbed?

Interception and uptake by plants decreases]

Soil water increases

Stream flow (peak flows, total annual flow) increases

What are the effects of forest disturbance on nutrient uptake over time?

Plant uptake decreases

Decomposition increases

nutrient availability increases (assart effect)

Combined effects of disturbance?

Nutrient concentration in stream flow increases

total nutrient losses in streamflow increases

What was the hubbard brook experimental watershed?

A test shed that was harvested and treated with herbicide to prevent regrowth

demonstrated role of vegetation in retraining soil nutrients

What are the effects of forest succession on nutrient regime?

• forest regrows- nutrient uptake increases, decomp declines

• Forest floor rebuilds- nutrient availability levels, leaching losses decline, streamflow losses decline