I guess this has something to do with soil. Didn’t see a nutrient cycle forum so here goes.
While learning about holistic management, an interesting element of the nutrient cycle was brought up, gravity. Basically, nutrients at higher elevations tend to get soaked up by water and then by plants further down in elevation leaving the top with less and less nutrients as time goes on. I believe it was Allan Savory who made it known to me that animals close this gap. They tend to eat in valley’s and at night, due to predator pressure, they go up in elevation and produce manure that starts at the top and moves its way down. This cycle repeats.
This lead me to thinks about the nutrient cycle on a larger scale. When this cycle occurs, some nutrients will probably make their way to tributaries, streams, rivers, deltas, and the ocean. Over time this builds up and lots of silt and nutrients reach down river. Though I can’t seem to think of how nature pushes these nutrients back upriver. It seems to me that migratory animals are the most likely solution, but when I think about it i can only imagine a roughly equal energy swap between the locations of the migratory animals and they eventually just end up bring energy from the upstream location back downstream. Any thoughts?
I'm going to say that most of the nutrients are not returned up hill at all. Think of the wonderfully fertile land on either side of the Nile for example, the fertility is brought in when the river floods, that fertility is brought in from 100's or even 1000's of miles away none or at least very little of that is ever going to make it back to the source.
To understand where most of the fertility on the hills is coming from you need to look down. but not very far a few feet at most. With the exception of Nitrogen (made from the air) most of the nutrients a ecosystem needs come from rocks being decomposed, on a high mountain ridge that decomposition is mainly by mechanical weathering, the actions of rain wind and frost breaking down the rocks into their constituent parts. As you come down from the cold heights you will find lichens and mosses, these secrete organic acids (and other things) that help break down the rocks they live on and provide them with nutrients, however physical weathering still plays a large part. Further still down the hill the bedrock is covered in soil and physical weathering processes are very slow or non existent, instead chemical weathering from the secretions of plant roots, fungi and the bacteria that live with them break down the rocks and release the trapped nutrients. When you get right down into the valleys and the soils are deep the bedrock is pretty well protected from all weathering and there the nutrients are brought in by gravity as you state.
If you want to look on an even larger scale of nutrient recycling then it gets geological, those "lost" nutrients that are washed out the mouth of the river fall as sediment onto the sea bed and eventually are buried and turned into rock, then as the continents move they can be uplifted and become the source for the beginning of the above cycle, the rocks that form the summit of Everest were once in a warm shallow sea. (apologies if I am trying to teach my grandmother to suck eggs here)